Everything you need to start with Geant4!
Geant4 source code and installers are available for download for all versions!
Documentation for Geant4, along with tutorials and guides, are available online.
Main reference papers for Geant4:
- Recent Developments in Geant4, J. Allison et al., Nucl. Instrum. Meth. A 835 (2016) 186-225
- Geant4 Developments and Applications, J. Allison et al., IEEE Trans. Nucl. Sci. 53 (2006) 270-278
- Geant4 - A Simulation Toolkit, S. Agostinelli et al., Nucl. Instrum. Meth. A 506 (2003) 250-303