Much can be said about the processes in PYTHIA and the way they are generated. Therefore the material has been split into three sections. In the current one the philosophy underlying the event generation scheme is presented. Here we provide a generic description, where some special cases are swept under the carpet. In the next section, the existing processes are enumerated, with some comments about applications and limitations. Finally, in the third section the generation routines and common-block switches are described.
The section starts with a survey of parton distributions, followed by a detailed description of the simple and hard subprocess generation schemes, including pairs of resonances. This is followed by a few comments on more complicated configurations, and on nonperturbative processes.