Thepeg, Herwig++ and Ariadne

Monte Carlo Event Generators (EGs) have developed into essential tools in High Energy Physics. Without them it is questionable if it at all would be possible to embark on large scale experiments such as the LHC. Although the current EGs work satisfactorily, the next generation of experiments will substantially increase the demands both on the physics models implemented in the EGs and on the underlying software technology. The current EGs are typically written in Fortran and their basic structure was designed almost two decades ago. Meanwhile there has been a change in programming paradigm, towards object oriented methodology in general and C++ in particular. This applies to almost all areas of highenergy physics, but in particular for the LHC program, where all detector simulation and analysis is based on C++. When designing the next generation of EGs it is therefore natural to use C++. Below is a brief description of the THEPEG [1] project for designing a general framework in C++ for implementing EG models, and also the HERWIG++ and ARIADNE programs which uses THEPEG to implement their respective physics models.