Geant4 and its validation

Geant4 is an object-oriented toolkit for simulating the passage of particles through matter. At the very heart of Geant4 there is a wide set of complementary, and sometimes alternative, physics models which describe the basic interaction of particles with matter. After a review of the main characteristics of the toolkit and a status report of the current activities, the results of a series of detailed tests for the quantitative validation of the electromagnetic models of Geant4 are presented. Such precision tests demonstrate the reliability of the physics models provided in Geant4 and are hence particularly relevant for critical applications of simulation models.