Recent theories of galaxy formation.

The paper reviews observational data, describes how galaxies may originate in a standard big-bang model, and considers several detailed theories of formation. Topics include the formation of galaxies from small inhomogeneities in the early universe, the collapse picture of galaxy formation, dissipation models for ellipticals, and dissipationless collapse models for elliptical galaxies. Important new ideas involving violent relaxation, dynamical friction, heavy halos, cosmological infall, and angular momentum via tidal interactions are noted. It is pointed out that several theoretical models have such a large number of legitimate free variable that all these models can be made to fit the observational data.