Geant4[1][2][3][4] (for GEometry ANd Tracking) is a platform for "the simulation of the passage of particles through matter" using Monte Carlo methods.

It is the successor of the GEANT series of software toolkits developed by The Geant4 Collaboration, and the first to use object oriented programming (in C++).

Geant4 includes facilities for handling geometry, tracking, detector response, run management, visualization and user interface.

Since release 10.0, Geant4 implements multithreading,[4] making use of thread-local storage to allow for efficient generation of simulated events in parallel.

Because of its general purpose nature, Geant4 is well suited for development of computational tools for analysing interactions of particle with matter in many areas.