  I review the current status of theoretical studies of galaxy formation. I
outline the importance of the physics of baryonic component in galaxy formation
by showing results obtained by using two major tools, semi-analytical
approaches and cosmological simulations. In particular, I emphasis on roles of
feedback in galaxy formation and discuss whether apparent conflictions between
the standard theory of structure formation, the cold dark matter model, and
observations can be solved by the feedback. I also discuss future prospects in
numerical simulations of galaxy formation.
