 disc choppers, velocity selectors) and a growing variety of samples, allowing to perform virtual experiments including sophisticated setups like polarized neutrons in magnetic fields.Parameters specifying the instrument components can be given by means of a graphical user interface, which makes VITESS comparably easy to use and quick to learn for new users, while advanced users can contribute their own modules.The validity of VITESS simulations is tested by comparison with other neutron simulation packages and with measurements at neutron scattering facilities.