I present a model for galaxy formation based on the physics of two-phase ISM in pressure equilibrium. In this model gas cools or infalls from an external halo, fragmenting into small clouds. These coagulate to form giant molecular complexes, which collapse and form stars. Supernovae drive superbubbles into the hot phase. The effect of feedback depends on whether superbubbles are confined or blow out of the system before cooling. Depending on the density and geometry of the system, I obtain self-regulated systems, rapid starbursts or critical systems where the hot phase suddenly collapses.