  New models for the formation of disk galaxies are presented. I discuss the
contraints on galaxy formation that follow from fitting the model to the
near-infrared Tully-Fisher (TF) relation, with an emphasis on reproducing the
small amount of scatter observed. Once the parameters that describe the
supernova feedback are tuned to fit the slope of the observed TF relation, the
model reproduces the correct amount of TF scatter, and yields gas mass
fractions, mass-to-light ratios, and characteristic accelerations that are all
in excellent agreement with observations.
