  We present a study of Sisyphus cooling of molecules: the scattering of a
single-photon remove a substantial amount of the molecular kinetic energy and
an optical pumping step allow to repeat the process. A review of the produced
cold molecules so far indicates that the method can be implemented for most of
them, making it a promising method able to produce a large sample of molecules
at sub-mK temperature. Considerations of the required experimental parameters,
for instance the laser power and linewidth or the trap anisotropy and
dimensionality, are given. Rate equations, as well as scattering and dipolar
forces, are solved using Kinetic Monte Carlo methods for several lasers and
several levels. For NH molecules, such detailed simulation predicts a 1000-fold
temperature reduction and an increase of the phase space density by a factor of
10^7 . Even in the case of molecules with both low Franck-Condon coefficients
and a non-closed pumping scheme, 60% of trapped molecules can be cooled from
100 mK to sub-mK temperature in few seconds. Additionally, these methods can be
applied to continuously decelerate and cool a molecular beam
