I will briefly review our understanding of disk galaxy formation, highlighting what we think we know and what we would like to know. Our knowledge of galaxy formation is driven by observations. Numerical simulations are a powerful tool to study these problems, but they are still unable to answer some of the most simple questions about how galaxies form and evolve. However, they are rapidly becoming more sophisticated and accurate-for example we can now resolve molecular cloud formation within disk galaxies that form within a hierarchical cosmological context. Optimistically, we are within reach of achieving a reasonable understanding of the origin of the Hubble sequence within the next decade.