Each type of particle, by definition, is special. The special property of neutrinos is that they are penetrating. This has made their discovery and the understanding of their properties elusive, but it has also made them a useful tool in the study of particles and their interactions. In astrophysics, on account of this property, neutrinos provide an important means for energy transfer and permit insight into the interior of stars hidden to other radiation. The special conditions in space permit, in turn, the study of neutrino properties not possible in the laboratory.