diff --git a/Tracking/TrkTools/TrkToolInterfaces/TrkToolInterfaces/ITruthToTrack.h b/Tracking/TrkTools/TrkToolInterfaces/TrkToolInterfaces/ITruthToTrack.h
index ff2438d11c26c3bfb67a77c661bd0f8eba823351..2e0801ba13a2cfc9328bf94593425365eabe9026 100644
--- a/Tracking/TrkTools/TrkToolInterfaces/TrkToolInterfaces/ITruthToTrack.h
+++ b/Tracking/TrkTools/TrkToolInterfaces/TrkToolInterfaces/ITruthToTrack.h
@@ -51,7 +51,7 @@ namespace Trk {
      *  object. (Wrapping it into a smart pointer may be the most
      *  convenient way to make sure the memory is freed.)
      */
-    virtual const Trk::TrackParameters* makeProdVertexParameters(const HepMC::GenParticle* part) const = 0;
+    virtual const Trk::TrackParameters* makeProdVertexParameters(HepMC::ConstGenParticlePtr part) const = 0;
     virtual const Trk::TrackParameters* makeProdVertexParameters(const xAOD::TruthParticle* part) const = 0;
 
     /** This function extrapolates track to the perigee, and returns
@@ -61,7 +61,7 @@ namespace Trk {
      * operator new.  The caller is responsible for deletion of the
      * object.
      */
-    virtual const Trk::TrackParameters* makePerigeeParameters(const HepMC::GenParticle* part) const = 0;
+    virtual const Trk::TrackParameters* makePerigeeParameters(HepMC::ConstGenParticlePtr part) const = 0;
     virtual const Trk::TrackParameters* makePerigeeParameters(const xAOD::TruthParticle* part) const = 0;
 
   };
diff --git a/Tracking/TrkTools/TrkToolInterfaces/TrkToolInterfaces/ITruthTrajectoryBuilder.h b/Tracking/TrkTools/TrkToolInterfaces/TrkToolInterfaces/ITruthTrajectoryBuilder.h
index 61e708ffe730eb9a70a435936e12d8ac139059b4..b67b81d0c43d85216fcf404bb4a09a483a980364 100644
--- a/Tracking/TrkTools/TrkToolInterfaces/TrkToolInterfaces/ITruthTrajectoryBuilder.h
+++ b/Tracking/TrkTools/TrkToolInterfaces/TrkToolInterfaces/ITruthTrajectoryBuilder.h
@@ -29,13 +29,13 @@ namespace Trk {
     /** Build a TruthTrajectory this particle belongs to.  
      *  The result may be an empty TruthTrajectory (in case input did not pass the cuts).
      */
-    virtual void buildTruthTrajectory(TruthTrajectory *result, const HepMC::GenParticle *input) const = 0;
+    virtual void buildTruthTrajectory(TruthTrajectory *result, HepMC::ConstGenParticlePtr input) const = 0;
 
     /** Previous particle on the truth trajectory or 0 */
-    virtual const HepMC::GenParticle *getMother(const HepMC::GenParticle *part) const = 0;
+    virtual HepMC::ConstGenParticlePtr getMother(HepMC::ConstGenParticlePtr part) const = 0;
 
     /** Next particle on the truth trajectory or 0 */
-    virtual const HepMC::GenParticle *getDaughter(const HepMC::GenParticle *part) const = 0;
+    virtual HepMC::ConstGenParticlePtr getDaughter(HepMC::ConstGenParticlePtr part) const = 0;
   };
   
 } // namespace Trk
diff --git a/Tracking/TrkTools/TrkTruthCreatorTools/src/DecayInFlyTruthTrajectoryBuilder.cxx b/Tracking/TrkTools/TrkTruthCreatorTools/src/DecayInFlyTruthTrajectoryBuilder.cxx
index 9e25de02879fa589d7d07209f5d99d36d73505c4..6752fe0d1b6a73086382770d40aaf903573d5b5a 100644
--- a/Tracking/TrkTools/TrkTruthCreatorTools/src/DecayInFlyTruthTrajectoryBuilder.cxx
+++ b/Tracking/TrkTools/TrkTruthCreatorTools/src/DecayInFlyTruthTrajectoryBuilder.cxx
@@ -71,34 +71,32 @@ buildTruthTrajectory(TruthTrajectory *result, HepMC::ConstGenParticlePtr input)
 DecayInFlyTruthTrajectoryBuilder::MotherDaughter
 DecayInFlyTruthTrajectoryBuilder::truthTrajectoryCuts(HepMC::ConstGenVertexPtr vtx) const
 {
-  HepMC::GenParticlePtr mother{nullptr};
-  HepMC::GenParticlePtr daughter{nullptr};
-  // only truth vertices with 1 incoming particle
+  HepMC::ConstGenParticlePtr mother{nullptr};
+  HepMC::ConstGenParticlePtr daughter{nullptr};
+     // only truth vertices with 1 incoming particle     
+      // Restrict to quasi-elastic processes (e.g. brems, delta-rays, pi->pi+Delta).
+      // 
+      // Require not more than 2 outgoing particles. Note that
+      // delta-rays for primary==electron is a special case, because we have two
+      // outgoing particles with the same PDG id.  The "correct" one
+      // is that with the higher energy (NOT pt).
+      // 
+      // allow 1 outgoing to cover possible vertexes from interaction in detector material
 #ifdef HEPMC3
-  if(vtx && (vtx->particles_in().size() == 1)) {
+  if(vtx && (vtx->particles_in().size() == 1) && (vtx->particles_out().size() <= 2)  ) {
 
     mother = vtx->particles_in().front();
 #else 
-  if(vtx && (vtx->particles_in_size() == 1)) {
+  if(vtx && (vtx->particles_in_size() == 1) && (vtx->particles_out_size() <= 2) ) {
 
     mother = *vtx->particles_in_const_begin();
 #endif    
     // Allow status code 1 and 2.  E.g. a pion that produced a long track can decay  outside of InDet and have status==2.
     if( mother && (mother->status() < 3) ) {
-    
-      // Restrict to quasi-elastic processes (e.g. brems, delta-rays, pi->pi+Delta).
-      // 
-      // Require not more than 2 outgoing particles. Note that
-      // delta-rays for primary==electron is a special case, because we have two
-      // outgoing particles with the same PDG id.  The "correct" one
-      // is that with the higher energy (NOT pt).
-      // 
-      // allow 1 outgoing to cover possible vertexes from interaction in detector material
-      if (vtx->particles_out_size() <= 2) {
 
 	int num_passed_cuts = 0;
-	HepMC::GenParticlePtr passed_cuts{nullptr};
-	for(HepMC::GenParticlePtr candidate: *vtx){
+	HepMC::ConstGenParticlePtr passed_cuts{nullptr};
+	for(HepMC::ConstGenParticlePtr candidate: *vtx){
 	  if(candidate->pdg_id() == mother->pdg_id()) {
 
 	    if(passed_cuts && (mother->pdg_id() == 11)) { // second negative electron is a special case
@@ -121,8 +119,6 @@ DecayInFlyTruthTrajectoryBuilder::truthTrajectoryCuts(HepMC::ConstGenVertexPtr v
 	if(num_passed_cuts==1) { // disallow hadronic pi->N*pi etc.
 	  daughter = passed_cuts;
 	}
-
-      } // if (vtx->particles_out_size() <= 2)
     } // if( mother && (mother->status() == 1) )
   }
   
diff --git a/Tracking/TrkTools/TrkTruthCreatorTools/src/DetailedTrackTruthBuilder.cxx b/Tracking/TrkTools/TrkTruthCreatorTools/src/DetailedTrackTruthBuilder.cxx
index e560005102d3c15c47fc65608d53cfdb865f4dab..04e2724ff88ce47df8cfa86cb09da857d20beca7 100755
--- a/Tracking/TrkTools/TrkTruthCreatorTools/src/DetailedTrackTruthBuilder.cxx
+++ b/Tracking/TrkTools/TrkTruthCreatorTools/src/DetailedTrackTruthBuilder.cxx
@@ -165,7 +165,7 @@ buildDetailedTrackTruth(DetailedTrackTruthCollection *output,
       const TruthTrajectory& t = i->second.trajectory();
       msg(MSG::VERBOSE)<<"Particles on the trajectory:\n";
       for(unsigned k=0; k<t.size(); ++k) {
-	msg(MSG::VERBOSE)<<*t[k]<<"\n";
+	msg(MSG::VERBOSE)<<t[k]<<"\n";
       }
       msg(MSG::VERBOSE)<<"\n"<<endmsg;
     }
@@ -353,12 +353,12 @@ void DetailedTrackTruthBuilder::addTrack(DetailedTrackTruthCollection *output,
   while(!seeds.empty()) {
     HepMcParticleLink link = *seeds.begin();
     Sprout current_sprout;
-    std::queue<const HepMC::GenParticle*> tmp;
+    std::queue<HepMC::ConstGenParticlePtr> tmp;
     ExtendedEventIndex eventIndex(link, proxy);
     const HepMC::GenParticle *current = link.cptr();
 
     do {
-      HepMcParticleLink curlink( eventIndex.makeLink(current->barcode(), proxy));
+      HepMcParticleLink curlink( eventIndex.makeLink(HepMC::barcode(current), proxy));
 
       // remove the current particle from the list of particles to consider (if it is still there)
       seeds.erase(curlink);
@@ -410,7 +410,7 @@ void DetailedTrackTruthBuilder::addTrack(DetailedTrackTruthCollection *output,
     // This may add only hits that are *not* on the current track.
     // Thus no need to update stats track and stats common.
 
-    const HepMC::GenParticle* current = *s->second.begin();
+    auto current = *s->second.begin();
     while( (current = m_truthTrajBuilder->getDaughter(current)) ) {
       s->second.push_front(current);
     }
diff --git a/Tracking/TrkTruthTracks/TrkTruthTrackInterfaces/TrkTruthTrackInterfaces/IPRD_TruthTrajectoryBuilder.h b/Tracking/TrkTruthTracks/TrkTruthTrackInterfaces/TrkTruthTrackInterfaces/IPRD_TruthTrajectoryBuilder.h
index 309d14623515dc70d45915a2e352ff3a53dfc5f3..58365fe2213370bbc6ecbf7fcab59b5ccf588974 100644
--- a/Tracking/TrkTruthTracks/TrkTruthTrackInterfaces/TrkTruthTrackInterfaces/IPRD_TruthTrajectoryBuilder.h
+++ b/Tracking/TrkTruthTracks/TrkTruthTrackInterfaces/TrkTruthTrackInterfaces/IPRD_TruthTrajectoryBuilder.h
@@ -38,7 +38,7 @@ namespace Trk {
        static const InterfaceID& interfaceID() { return IID_IPRD_TruthTrajectoryBuilder; }
 
        /** return a vector of PrepRawData trajectories - uses internal cache**/
-       virtual const std::map< const HepMC::GenParticle*, PRD_TruthTrajectory >& truthTrajectories() const = 0;
+       virtual const std::map< HepMC::ConstGenParticlePtr, PRD_TruthTrajectory >& truthTrajectories() const = 0;
        
        /** Event refresh - can't be an IIncident, because it has to run after PRD creation and PRD truth creation */
        virtual StatusCode refreshEvent() = 0;       
diff --git a/Tracking/TrkTruthTracks/TrkTruthTrackInterfaces/TrkTruthTrackInterfaces/PRD_TruthTrajectory.h b/Tracking/TrkTruthTracks/TrkTruthTrackInterfaces/TrkTruthTrackInterfaces/PRD_TruthTrajectory.h
index 21ff251f2e43dd3129747a08aa3ed830668a7b0f..2d3a9df02060a658c868595598f4fd0bfacf4c3e 100644
--- a/Tracking/TrkTruthTracks/TrkTruthTrackInterfaces/TrkTruthTrackInterfaces/PRD_TruthTrajectory.h
+++ b/Tracking/TrkTruthTracks/TrkTruthTrackInterfaces/TrkTruthTrackInterfaces/PRD_TruthTrajectory.h
@@ -28,7 +28,7 @@ namespace Trk {
       
      /**  public members */ 
      std::vector<const Trk::PrepRawData* > prds;
-     const HepMC::GenParticle*             genParticle;
+     HepMC::ConstGenParticlePtr             genParticle;
      size_t                                nDoF;
 
      /** defualt constructor */
@@ -39,7 +39,7 @@ namespace Trk {
      
      /** fast constructor */
      PRD_TruthTrajectory( const std::vector<const Trk::PrepRawData* >& prdVec,
-                          const HepMC::GenParticle* gP    = 0,
+                          HepMC::ConstGenParticlePtr gP    = nullptr,
                           size_t numberOfDegreesOfFreedom = 0) :
       prds(prdVec),
       genParticle(gP),
diff --git a/Tracking/TrkTruthTracks/TrkTruthTrackTools/src/PRD_TruthTrajectoryBuilder.cxx b/Tracking/TrkTruthTracks/TrkTruthTrackTools/src/PRD_TruthTrajectoryBuilder.cxx
index 7b60f9c4c5d8753febe9c5c73af442944d4b9255..628c472caefaa02c3d55093692e67009b69c79e7 100644
--- a/Tracking/TrkTruthTracks/TrkTruthTrackTools/src/PRD_TruthTrajectoryBuilder.cxx
+++ b/Tracking/TrkTruthTracks/TrkTruthTrackTools/src/PRD_TruthTrajectoryBuilder.cxx
@@ -97,7 +97,7 @@ StatusCode Trk::PRD_TruthTrajectoryBuilder::refreshEvent()  {
    
 }
 
-const std::map< const HepMC::GenParticle*, Trk::PRD_TruthTrajectory >& Trk::PRD_TruthTrajectoryBuilder::truthTrajectories() const {
+const std::map<HepMC::ConstGenParticlePtr, Trk::PRD_TruthTrajectory >& Trk::PRD_TruthTrajectoryBuilder::truthTrajectories() const {
     // ndof
     size_t ndofTotal = 0;
     size_t ndof      = 0;
@@ -111,7 +111,7 @@ const std::map< const HepMC::GenParticle*, Trk::PRD_TruthTrajectory >& Trk::PRD_
         PRD_MultiTruthCollection::const_iterator prdMtCIterE = (*pmtCollIter)->end();
         for ( ; prdMtCIter != prdMtCIterE; ++ prdMtCIter ){
             // check if entry exists and if   
-            const HepMC::GenParticle* curGenP       = (*prdMtCIter).second;
+            auto curGenP       = (*prdMtCIter).second;
             Identifier                curIdentifier = (*prdMtCIter).first;
             // apply the min pT cut 
             if ( curGenP->momentum().perp() < m_minPt ) continue;
@@ -123,7 +123,7 @@ const std::map< const HepMC::GenParticle*, Trk::PRD_TruthTrajectory >& Trk::PRD_
             // stuff it into the trajectory if you found a PRD
             if (prd){
                 // try to find the entry for this GenParticle 
-                std::map< const HepMC::GenParticle*, PRD_TruthTrajectory >::iterator prdTrajIter = m_gpPrdTruthTrajectories.find(curGenP);
+                auto prdTrajIter = m_gpPrdTruthTrajectories.find(curGenP);
                 if ( prdTrajIter ==  m_gpPrdTruthTrajectories.end() ){
                     // first PRD associated to this: create PRD_TruthTrajectory object
                     Trk::PRD_TruthTrajectory newPrdTruthTrajectory;
@@ -147,8 +147,8 @@ const std::map< const HepMC::GenParticle*, Trk::PRD_TruthTrajectory >& Trk::PRD_
     }
     // PART 2 --------------------------------------------------------------------------------------------------------
     // loop through the provided list of manipulators ( sorter is included )
-    std::map< const HepMC::GenParticle*, PRD_TruthTrajectory >::iterator prdTruthTrajIter  = m_gpPrdTruthTrajectories.begin();
-    std::map< const HepMC::GenParticle*, PRD_TruthTrajectory >::iterator prdTruthTrajIterE = m_gpPrdTruthTrajectories.end();
+    auto prdTruthTrajIter  = m_gpPrdTruthTrajectories.begin();
+    auto prdTruthTrajIterE = m_gpPrdTruthTrajectories.end();
     for ( ; prdTruthTrajIter != prdTruthTrajIterE; ++prdTruthTrajIter ){
     //std::cout << "sorting, barcode: " << prdTruthTrajIter->first->barcode() << std::endl;
         if ( m_prdTruthTrajectoryManipulators.size() ){
diff --git a/Tracking/TrkTruthTracks/TrkTruthTrackTools/src/PRD_TruthTrajectoryBuilder.h b/Tracking/TrkTruthTracks/TrkTruthTrackTools/src/PRD_TruthTrajectoryBuilder.h
index 3199d6c9ed38d7c6ef22da7037ba8be0badc7f4f..6112ea9f8370335480e1159fdd42d94f4b5d20e1 100644
--- a/Tracking/TrkTruthTracks/TrkTruthTrackTools/src/PRD_TruthTrajectoryBuilder.h
+++ b/Tracking/TrkTruthTracks/TrkTruthTrackTools/src/PRD_TruthTrajectoryBuilder.h
@@ -53,7 +53,7 @@ namespace Trk {
        StatusCode  finalize();
 
        /** return a vector of PrepRawData trajectories - uses internal cache**/
-       const std::map< const HepMC::GenParticle*, PRD_TruthTrajectory >& truthTrajectories() const;
+       const std::map< HepMC::ConstGenParticlePtr, PRD_TruthTrajectory >& truthTrajectories() const;
 
        /** Event refresh - can't be an IIncident, because it has to run after PRD creation and PRD truth creation */
        StatusCode refreshEvent();
@@ -71,7 +71,7 @@ namespace Trk {
         
 	Gaudi::Property<double>                             m_minPt {this,"MinimumPt",400.,"minimum pT to be even considered"};
 	Gaudi::Property<bool>                               m_geantinos {this,"Geantinos",false,"Track geantinos or not"};
-        mutable std::map< const HepMC::GenParticle*, PRD_TruthTrajectory > m_gpPrdTruthTrajectories; //!< the cache for the return (cleared by Incident)
+        mutable std::map< HepMC::ConstGenParticlePtr, PRD_TruthTrajectory > m_gpPrdTruthTrajectories; //!< the cache for the return (cleared by Incident)
         
   };
 
diff --git a/Tracking/TrkTruthTracks/TrkTruthTrackTools/src/TruthTrackBuilder.cxx b/Tracking/TrkTruthTracks/TrkTruthTrackTools/src/TruthTrackBuilder.cxx
index 1940d483abe38acde00dfa9fac5bbdf5ed0def2d..bda9841b728f682f5bd609f57985ca033fcab1db 100644
--- a/Tracking/TrkTruthTracks/TrkTruthTrackTools/src/TruthTrackBuilder.cxx
+++ b/Tracking/TrkTruthTracks/TrkTruthTrackTools/src/TruthTrackBuilder.cxx
@@ -130,7 +130,7 @@ Trk::Track* Trk::TruthTrackBuilder::createTrack(const PRD_TruthTrajectory& prdTr
     ATH_MSG_VERBOSE("The PRD Truth trajectory contains " << prdTraj.prds.size() << " PRDs.");
 
     // get the associated GenParticle
-    const HepMC::GenParticle* genPart = prdTraj.genParticle;
+    auto genPart = prdTraj.genParticle;
     if (!genPart) {
         ATH_MSG_WARNING("No GenParticle associated to this PRD_TruthTrajectory. Ignoring track creation.");
         return 0;
diff --git a/Tracking/TrkValidation/TrkValAlgs/TrkValAlgs/TrackValidationNtupleWriter.h b/Tracking/TrkValidation/TrkValAlgs/TrkValAlgs/TrackValidationNtupleWriter.h
index b5fe26995e4d217a39997ba7531c8584abfe75c0..98e06ad91b6e7c9d0bc09fea08d34bfe6a6b2c50 100644
--- a/Tracking/TrkValidation/TrkValAlgs/TrkValAlgs/TrackValidationNtupleWriter.h
+++ b/Tracking/TrkValidation/TrkValAlgs/TrkValAlgs/TrackValidationNtupleWriter.h
@@ -96,7 +96,7 @@ protected:
   bool                      m_doTruth;                     //!< Switch to turn on / off truth
   bool                      m_doTrackParticle;             //!  Switch to turn on/pff recording track particle trees into Ntuple 
 
-  const HepMC::GenParticle* m_visibleParticleWithoutTruth; //!< cludge to treat G4's "fake fakes"
+  HepMC::GenParticlePtr m_visibleParticleWithoutTruth; //!< cludge to treat G4's "fake fakes"
   std::vector<unsigned int>           m_nTrackTreeRecords;
   std::vector<TTree*>       m_trees;                 //!< Pointer to the NTuple trees (one for each input track collection)
   TTree*                    m_eventLinkTree;         //!< pointer to event-wise ntuple trees (one for all input track collections + truth)
diff --git a/Tracking/TrkValidation/TrkValAlgs/src/RecMomentumQualityValidation.cxx b/Tracking/TrkValidation/TrkValAlgs/src/RecMomentumQualityValidation.cxx
index 6b6d9248f5e57bb4e1b122ba8f078fe6b1438938..9e37c70845e06b7bed5f0c87947a3954c6bf2e8f 100644
--- a/Tracking/TrkValidation/TrkValAlgs/src/RecMomentumQualityValidation.cxx
+++ b/Tracking/TrkValidation/TrkValAlgs/src/RecMomentumQualityValidation.cxx
@@ -135,7 +135,7 @@ StatusCode Trk::RecMomentumQualityValidation::execute()
 
       // find matching truth particle
       const TrackTruth* trackTruth = 0;
-      const HepMC::GenParticle* genParticle = 0;
+      HepMC::ConstGenParticlePtr genParticle{nullptr};
       TrackTruthCollection::const_iterator truthIterator 
         = trackTruthCollection->find( trackIterator - (*trackCollection).begin() );
       if ( truthIterator == trackTruthCollection->end() ){
diff --git a/Tracking/TrkValidation/TrkValAlgs/src/TrackValidationNtupleWriter.cxx b/Tracking/TrkValidation/TrkValAlgs/src/TrackValidationNtupleWriter.cxx
index d24e097589807a0d3a9daac874f4d3879ceb6f05..7ebe04335e8ef9c62bcd553ed5aee2ffe5f405af 100644
--- a/Tracking/TrkValidation/TrkValAlgs/src/TrackValidationNtupleWriter.cxx
+++ b/Tracking/TrkValidation/TrkValAlgs/src/TrackValidationNtupleWriter.cxx
@@ -219,7 +219,7 @@ StatusCode Trk::TrackValidationNtupleWriter::initialize() {
         sc = m_truthNtupleTool->initBranches(m_trackTruthClassifiers, include_jets, m_inputTrackCollection);
         if (sc.isFailure()) return sc;
 
-        m_visibleParticleWithoutTruth = new HepMC::GenParticle(HepLorentzVector(), 0);
+        m_visibleParticleWithoutTruth = HepMC::newGenParticlePtr(HepMC::FourVector(), 0);
 
     } // if truth is activated
 
@@ -332,7 +332,7 @@ StatusCode Trk::TrackValidationNtupleWriter::execute() {
 
     unsigned int nTruthTreeRecordsAtCurrentEvent = 0;
     std::vector<Trk::ValidationTrackTruthData>  truthData;
-    std::vector<const HepMC::GenParticle*>*  selecParticles = 0;
+    std::vector<HepMC::ConstGenParticlePtr>*  selecParticles = nullptr;
     //std::vector<const Trk::TrackParameters*> extrapolatedTruthPerigees;
     //std::vector<std::vector<unsigned int> >  classifications;
     std::vector< Trk::GenParticleJet >*      genParticleJets = 0;
@@ -377,7 +377,7 @@ StatusCode Trk::TrackValidationNtupleWriter::execute() {
                 if ( genParticle->production_vertex() )
                   {
                     generatedTrackPerigee = m_truthToTrack->makePerigeeParameters( genParticle );
-                    if (generatedTrackPerigee == NULL && genParticle->barcode() > 1000000 ) {
+                    if (generatedTrackPerigee == NULL && HepMC::barcode(genParticle) > 1000000 ) {
                       ATH_MSG_DEBUG ("No perigee available for interacting truth particle."
                                      <<" -> This is OK for particles from the TrackRecord, but probably"
                                      <<" a bug for production vertex particles.");
@@ -389,7 +389,7 @@ StatusCode Trk::TrackValidationNtupleWriter::execute() {
                 partData.classifications.reserve(m_trackTruthClassifiers.size());
                 for (unsigned int toolIndex = 0 ; toolIndex < m_trackTruthClassifiers.size(); ++toolIndex ) 
                   {
-                    partData.classifications.push_back(m_trackTruthClassifiers[toolIndex]->classify(*genParticle));
+                    partData.classifications.push_back(m_trackTruthClassifiers[toolIndex]->classify(genParticle));
                   }
                 // resize the truth to track vectors to the number of input track collections:
                 partData.truthToTrackIndices.resize(m_inputTrackCollection.size());
@@ -594,7 +594,7 @@ StatusCode Trk::TrackValidationNtupleWriter::writeTrackData(unsigned int trackCo
             if (m_doTruth){
                 // find matching truth particle
                 const TrackTruth* trackTruth = 0;
-                const HepMC::GenParticle* genParticle = 0;
+                HepMC::ConstGenParticlePtr genParticle{nullptr};
                 TrackTruthCollection::const_iterator truthIterator = trackTruthCollection->find( trackIterator - (*tracks).begin() );
                 if ( truthIterator == trackTruthCollection->end() ){
                   ATH_MSG_DEBUG ("No matching truth particle found for track");
diff --git a/Tracking/TrkValidation/TrkValInterfaces/TrkValInterfaces/IGenParticleJetFinder.h b/Tracking/TrkValidation/TrkValInterfaces/TrkValInterfaces/IGenParticleJetFinder.h
index fde30d484a15d4eae8a98ffd6076812fb75f75a6..b16a3ab46f3cd913d025816a6b43ca4a7d291c06 100644
--- a/Tracking/TrkValidation/TrkValInterfaces/TrkValInterfaces/IGenParticleJetFinder.h
+++ b/Tracking/TrkValidation/TrkValInterfaces/TrkValInterfaces/IGenParticleJetFinder.h
@@ -47,7 +47,7 @@ class IGenParticleJetFinder : virtual public IAlgTool {
         This method is a factory, i.e. vector ownership is given back and
         on failure condition returns NULL. */
     virtual std::vector< Trk::GenParticleJet >*  jetMCFinder
-      (std::vector <const HepMC::GenParticle *>& ) const=0;
+      (std::vector <HepMC::ConstGenParticlePtr>& ) const=0;
 
   };
 
diff --git a/Tracking/TrkValidation/TrkValInterfaces/TrkValInterfaces/IGenParticleSelector.h b/Tracking/TrkValidation/TrkValInterfaces/TrkValInterfaces/IGenParticleSelector.h
index 0e58912b073fef1eaf5768fab0b5e74f0144cf9e..ac8d6b138ee49476ea77a7ee7a8f76f287db502b 100644
--- a/Tracking/TrkValidation/TrkValInterfaces/TrkValInterfaces/IGenParticleSelector.h
+++ b/Tracking/TrkValidation/TrkValInterfaces/TrkValInterfaces/IGenParticleSelector.h
@@ -33,7 +33,7 @@ class IGenParticleSelector : virtual public IAlgTool {
     static const InterfaceID& interfaceID();
     
     /** explain */
-    virtual std::vector<const HepMC::GenParticle *>*
+    virtual std::vector<HepMC::ConstGenParticlePtr>*
       selectGenSignal (const McEventCollection*) const=0;
   };
 
diff --git a/Tracking/TrkValidation/TrkValInterfaces/TrkValInterfaces/ITrackTruthClassifier.h b/Tracking/TrkValidation/TrkValInterfaces/TrkValInterfaces/ITrackTruthClassifier.h
index 56af45805d4908631248bcf821940a35cc15f72e..c557707b4470598e37cbd1be70f552b56d4d0b07 100644
--- a/Tracking/TrkValidation/TrkValInterfaces/TrkValInterfaces/ITrackTruthClassifier.h
+++ b/Tracking/TrkValidation/TrkValInterfaces/TrkValInterfaces/ITrackTruthClassifier.h
@@ -33,9 +33,9 @@ class ITrackTruthClassifier : virtual public IAlgTool {
     
     /** explain */
     virtual void initClassification(const McEventCollection&,
-                                    const std::vector<const HepMC::GenParticle *>*) const=0;
+                                    const std::vector<HepMC::ConstGenParticlePtr>*) const=0;
 
-    virtual unsigned int classify(const HepMC::GenParticle&) const = 0;
+    virtual unsigned int classify(HepMC::ConstGenParticlePtr) const = 0;
 
     virtual std::string nameOfClassifier() const = 0;
 
diff --git a/Tracking/TrkValidation/TrkValTools/TrkValTools/PrimaryTruthClassifier.h b/Tracking/TrkValidation/TrkValTools/TrkValTools/PrimaryTruthClassifier.h
index 496e2a09b8d731a26b207b1bac57f719ce27d894..c3eaf26f51fe65482bef104106a649cd2bcb0271 100644
--- a/Tracking/TrkValidation/TrkValTools/TrkValTools/PrimaryTruthClassifier.h
+++ b/Tracking/TrkValidation/TrkValTools/TrkValTools/PrimaryTruthClassifier.h
@@ -18,6 +18,7 @@
 #include "TrkValEvent/TruthClassificationDefs.h"
 
 #include "AtlasHepMC/GenParticle.h"
+#include "AtlasHepMC/SimpleVector.h"
 
 namespace Trk {
 
@@ -40,9 +41,9 @@ namespace Trk {
 
       /** explain */
       virtual void initClassification(const McEventCollection&,
-                                      const std::vector<const HepMC::GenParticle *>*) const;
+                                      const std::vector<HepMC::ConstGenParticlePtr>*) const;
 
-      virtual unsigned int classify(const HepMC::GenParticle&) const;
+      virtual unsigned int classify(HepMC::ConstGenParticlePtr) const;
 
       virtual std::string nameOfClassifier() const;
 
diff --git a/Tracking/TrkValidation/TrkValTools/src/PrimaryTruthClassifier.cxx b/Tracking/TrkValidation/TrkValTools/src/PrimaryTruthClassifier.cxx
index bd344c64e57067554318fcfd02eb0fcffc5a2dae..01c8f65d5657651eef274a69af00fb87f0d0351e 100644
--- a/Tracking/TrkValidation/TrkValTools/src/PrimaryTruthClassifier.cxx
+++ b/Tracking/TrkValidation/TrkValTools/src/PrimaryTruthClassifier.cxx
@@ -53,7 +53,7 @@ StatusCode Trk::PrimaryTruthClassifier::finalize() {
 
 void Trk::PrimaryTruthClassifier::initClassification
 (const McEventCollection& /*SimTracks*/,
- const std::vector<const HepMC::GenParticle *>* /*genSignal*/) const {
+ const std::vector<HepMC::ConstGenParticlePtr>* /*genSignal*/) const {
 
   // nothing to prepare as local data at start of collection analysis
   return;
@@ -62,7 +62,7 @@ void Trk::PrimaryTruthClassifier::initClassification
 //////////////////////////////////////////
 // classification from InDetRecStatistics
 //////////////////////////////////////////
-unsigned int Trk::PrimaryTruthClassifier::classify(const HepMC::GenParticle& genParticle) const {
+unsigned int Trk::PrimaryTruthClassifier::classify(HepMC::ConstGenParticlePtr genParticle) const {
 
  
   /* note on using HepMC::FourVector/3Vector against HepGeom::Point3D<double>: The versions from HepMC2 do not know
@@ -74,17 +74,17 @@ unsigned int Trk::PrimaryTruthClassifier::classify(const HepMC::GenParticle& gen
   bool  secondary=false;
   bool  truncated=false;
 
-  if (genParticle.production_vertex()) {
-    HepMC::FourVector      startVertex = genParticle.production_vertex()->position();
+  if (genParticle->production_vertex()) {
+    HepMC::FourVector      startVertex = genParticle->production_vertex()->position();
 
     // primary vertex inside innermost layer?
     if ( fabs(startVertex.perp()) < m_maxRStartPrimary 
          && fabs(startVertex.z()) < m_maxZStartPrimary)
       {
-        if (genParticle.end_vertex() == 0) {  
+        if (genParticle->end_vertex() == 0) {  
           primary=true;
         } else {
-          HepMC::FourVector endVertex = genParticle.end_vertex()->position();
+          HepMC::FourVector endVertex = genParticle->end_vertex()->position();
           if (  endVertex.perp()         > m_minREndPrimary 
                 || fabs(startVertex.z()) > m_minZEndPrimary)
             primary=true; else truncated = true;
@@ -93,10 +93,10 @@ unsigned int Trk::PrimaryTruthClassifier::classify(const HepMC::GenParticle& gen
     else if ( startVertex.perp()    <  m_maxRStartSecondary && 
               fabs(startVertex.z()) <  m_maxZStartSecondary)
       {
-        if (genParticle.end_vertex() == 0) {  
+        if (genParticle->end_vertex() == 0) {  
           secondary=true;
         } else {
-          HepMC::FourVector endVertex = genParticle.end_vertex()->position();
+          HepMC::FourVector endVertex = genParticle->end_vertex()->position();
           if (endVertex.perp()            > m_minREndSecondary
               || fabs(endVertex.z())      > m_minZEndSecondary) {
             secondary=true;
@@ -108,8 +108,7 @@ unsigned int Trk::PrimaryTruthClassifier::classify(const HepMC::GenParticle& gen
   if (truncated) return Trk::TruthClassification::Truncated;
   if (secondary) return Trk::TruthClassification::Secondary;
   if (primary) return Trk::TruthClassification::Primary;
-  ATH_MSG_DEBUG ( "Could not classify this particle: " 
-        << genParticle );
+  ATH_MSG_DEBUG ( "Could not classify this particle: " << genParticle );
   return Trk::TruthClassification::OutsideClassification;
 
 }
diff --git a/Tracking/TrkValidation/TrkVertexFitterValidationUtils/src/TrkPriVxPurityTool.cxx b/Tracking/TrkValidation/TrkVertexFitterValidationUtils/src/TrkPriVxPurityTool.cxx
index b0effec98c423cf4b5e65be44ff9108ef912bbe8..9a9d2eb64510eb8f5ecc197099a56e8900f46d8e 100755
--- a/Tracking/TrkValidation/TrkVertexFitterValidationUtils/src/TrkPriVxPurityTool.cxx
+++ b/Tracking/TrkValidation/TrkVertexFitterValidationUtils/src/TrkPriVxPurityTool.cxx
@@ -79,36 +79,47 @@ namespace Trk {
 //getting the signal event itself
                 McEventCollection::const_iterator it = mcCollection->begin();
                 const HepMC::GenEvent* genEvent= ( *it );
+#ifdef HEPMC3
+                if( genEvent->vertices().empty() ) {
+                  ATH_MSG_DEBUG( "No vertices found in first GenEvent" );
+                  return 0;
+                }
+               auto pv = genEvent->vertices()[0];
+#else
 //        std::cout<<"The ID of the first event of the collection: "<<genEvent->event_number()<<std::endl;
                 if( genEvent->vertices_empty() ) {
                   ATH_MSG_DEBUG( "No vertices found in first GenEvent" );
                   return 0;
                 }
+               auto pv = *(genEvent->vertices_begin());
+#endif
 
 //analysing the MC event to create PV candidate
 //first finding the vertex of primary pp interaction
-                HepMC::GenEvent::vertex_const_iterator pv = genEvent->vertices_begin();
 
 //and storing its position
-                CLHEP::HepLorentzVector pv_pos ( ( *pv )->position().x(),
-                                          ( *pv )->position().y(),
-                                          ( *pv )->position().z(),
-                                          ( *pv )->position().t() );
+                CLHEP::HepLorentzVector pv_pos ( pv ->position().x(),
+                                          pv ->position().y(),
+                                          pv ->position().z(),
+                                          pv ->position().t() );
                 double pv_r = pv_pos.perp();
                 double pv_z = pv_pos.z();
 
 // storing all the ids of vertices reasonably close to the primary one.
 // here the region of interest is selected.
-                std::map<int,HepMC::GenVertex *> vertex_ids;
-
-                for ( HepMC::GenEvent::vertex_const_iterator i = genEvent->vertices_begin();
-                      i != genEvent->vertices_end()  ;++i ) {
-                    CLHEP::HepLorentzVector lv_pos ( ( *i )->position().x(),
-                                              ( *i )->position().y(),
-                                              ( *i )->position().z(),
-                                              ( *i )->position().t() );
-                    if ( fabs ( lv_pos.perp() - pv_r ) <m_r_tol  && fabs ( lv_pos.z() - pv_z ) <m_z_tol ) {
-                        vertex_ids[ ( *i )->barcode() ]= ( *i );
+                std::map<int,HepMC::ConstGenVertexPtr> vertex_ids;
+#ifdef HEPMC3
+                for (auto vtx: genEvent->vertices()){
+#else
+                for ( HepMC::GenEvent::vertex_const_iterator i = genEvent->vertices_begin(); i != genEvent->vertices_end()  ;++i ) {
+                    auto vtx=*i;
+#endif
+                    CLHEP::HepLorentzVector lv_pos ( vtx->position().x(),
+                                              vtx->position().y(),
+                                              vtx->position().z(),
+                                              vtx->position().t() );
+                    if ( std::abs ( lv_pos.perp() - pv_r ) <m_r_tol  && std::abs ( lv_pos.z() - pv_z ) <m_z_tol ) {
+                        vertex_ids[ HepMC::barcode(vtx) ]= vtx;
                     }//end of accepted vertices check
                 }//end  of loop over all the vertices
 
@@ -128,7 +139,6 @@ namespace Trk {
 //looping over the tracks to find those matched to the GenParticle originating from signal PV
                 std::vector<Trk::VxTrackAtVertex *>::const_iterator vt = tracks->begin();
                 std::vector<Trk::VxTrackAtVertex *>::const_iterator ve = tracks->end();
-//         unsigned int total_size = 0;
                 unsigned int n_failed = 0;
                 std::vector<double> in_weights ( 0 );
                 std::vector<double> out_weights ( 0 );
@@ -147,7 +157,6 @@ namespace Trk {
                             // get to the original track particle
                             LinkToTrackParticleBase * tr_part = dynamic_cast< LinkToTrackParticleBase * > ( origLink );
                             if ( tr_part !=0  && tr_part->isValid()) {
-//                 ++total_size;
                 
 
                                 std::map< Rec::TrackParticleTruthKey, TrackParticleTruth>::const_iterator ttItr = trackParticleTruthCollection->end();
@@ -166,22 +175,22 @@ namespace Trk {
 
                                 if (ttItr != trackParticleTruthCollection->end() ) {
                                     const HepMcParticleLink& particleLink = ttItr->second.particleLink();
-                                    const HepMC::GenParticle* genParticle = particleLink.cptr();
+                                    HepMC::ConstGenParticlePtr genParticle = particleLink.cptr();
 
-                                    if(genParticle !=0) {
-                                        HepMC::GenEvent * tpEvent = genParticle->parent_event();
+                                    if(genParticle) {
+                                        auto tpEvent = genParticle->parent_event();
                                         if(tpEvent==genEvent) { 
-                                            const HepMC::GenVertex * pVertex(0);
-                                            if (genParticle!=0) pVertex = genParticle->production_vertex();
-                                            if ( pVertex != 0 ) {
+                                            HepMC::ConstGenVertexPtr pVertex{nullptr};
+                                            if (genParticle) pVertex = genParticle->production_vertex();
+                                            if ( pVertex) {
                                                 int link_pid = genParticle->pdg_id();
                                                 bool primary_track = false;
                                                 bool secondary_track = false;
                   
 //loop over the particles until decision is really taken
                                                 do {
-                                                    int tvrt_code = pVertex->barcode();
-                                                    std::map<int, HepMC::GenVertex *>::const_iterator idf_res = vertex_ids.find ( tvrt_code );
+                                                    int tvrt_code = HepMC::barcode(pVertex);
+                                                    auto idf_res = vertex_ids.find ( tvrt_code );
 
 //for the HepMcParticle Link, the signal event has an index 0.
 // tagging on it
@@ -193,11 +202,19 @@ namespace Trk {
 //this vertex is not from the central region.
 //checking whether it is a bremsstrahlung
 //if so, propagating track to its origin, otherwise rejecting it completely.
+#ifdef HEPMC3
+                                                        if ( pVertex->particles_in().size() == 1 ) {
+#else
                                                         if ( pVertex->particles_in_size() == 1 ) {
+#endif
 // one mother particle: is it a brem of some kind?
-                                                            HepMC::GenVertex::particles_in_const_iterator inp = pVertex->particles_in_const_begin() ;
-                                                            HepMC::GenVertex * tmpVertex_loc = ( *inp )->production_vertex();
-                                                            if ( ( *inp )->pdg_id() == link_pid  && tmpVertex_loc) {
+#ifdef HEPMC3
+                                                            auto inp = pVertex->particles_in()[0] ;
+#else
+                                                            auto inp =*(pVertex->particles_in_const_begin()) ;
+#endif
+                                                            auto tmpVertex_loc = inp ->production_vertex();
+                                                            if ( inp ->pdg_id() == link_pid  && tmpVertex_loc) {
 // seems like a brem (this can be generator/simulation dependent unfortunately)
 // continue iterating
                                                                 pVertex = tmpVertex_loc;