Low-mass particles such as neutrinos, axions, other Nambu-Goldstone bosons, gravitons, and so forth are produced in the hot and dense interior of stars. Therefore, astrophysical arguments constrain the properties of these particles in ways which are often complementary to cosmological arguments and to laboratory experiments. The most important stellar-evolution arguments are explained and the resulting particle-physics limits are reviewed in the context of other information from cosmology and laboratory experiments. ©1999 American Institute of Physics.