Geant4: simulation for the next generation of HEP experiments

GEANT4 (RD44) is a world-wide collaboration of scientists aiming to create the detec-tor simulation toolkit necessary for the next generation of HEP experiments. A large variety of requirements also come from heavy ions physics, CP violation physics, cosmic rays physics, medical applications and space science applications. In order to meet such requirements, a large degree of functionality and flexibility has to be provided. GEANT4 is exploiting Object Oriented Technology to achieve these goals. The most relevant Ob-ject Oriented methodologies have been studied and a large number of tools and libraries have been investigated and evaluated. An overview of the GEANT4 analysis and de-sign model will be given and the main components of the object models discussed. The main functionality of a first prototype will also be described. An overall view of the collaboration's structure and strategy will also be given.