ABSTRACT
This chapter presents some of the effects of the weak interaction in relation to the development of stars. The weak interaction largely determines the mass of the core, and thus the strength and fate of the shock wave formed by the supernova explosion. During the collapse to a neutron star or to a black hole, observation of the neutrino emission provides the only possibility for direct diagnosis of the events in the interior of the star. The neutrino spectrum with its flavours, its luminosities and its time dependence reflects the entire internal evolution and thus provides a simultaneous test for theories of star collapse and of the formation of neutron stars and black holes. The formation of neutron stars is one of the few instances where the weak interaction plays a crucial role in a macroscopic event in nature.
