  The US involvement in Geant4 started with its adoption by the BaBar
experiment at SLAC in 1997 and the subsequent creation of a group at SLAC
supporting BaBar and contributing to Geant4 development. SLAC has provided the
leadership of the international Geant4 Collaboration for the recent years and
carries major responsibilities for evolutionary development of the existing
code with work to implement multithreading and explore new application domains
as well as new technologies such as GPUs. This paper presents the current and
the future developments being carried by the SLAC Geant4 team.
