CompHEP is based on quantum theory of gauge fields, namely it uses the technique of squared Feynman diagrams at the tree-level approximation. By default, CompHEP includes the Standard Model Lagrangian in the unitarity and 't Hooft-Feynman gauges and several MSSM models. However users can create new physical models, based on different Lagrangians. There is a special tool for that - LanHEP. CompHEP is able to compute basically the LO cross sections and distributions with several particles in the final state (up to 6-7). It can take into account, if necessary, all QCD and EW diagrams, masses of fermions and bosons and widths of unstable particles. Processes computed by means of CompHEP can be interfaced to the Monte-Carlo generators PYTHIA and HERWIG as new external processes.