The dark matter that dominates the matter budget of the universe, and in particular the galactic mass budget, is considered to be non-dissipative. While the precise nature of the dark matter remains elusive, the hierarchical formation of non-dissipative dark potential wells in which baryons dissipate and condense into stars, has provided a successful model for many elements of the large-scale structure of the galaxy distribution [White & Rees1978]. Galaxy clustering can be explained in such a framework, as can the properties of the dark halos that are inferred, for example, from rotation curves, and of the intergalactic medium where neutral baryons in the form of the Lyman alpha forest provide a powerful probe of the weakly nonlinear regime. Tidal torques are generated by nonlinear interactions between neighbouring fluctuations and nascent halos. If the baryons conserve angular momentum as they dissipate kinetic energy and contract, disks spanning the observed size distribution are formed. The distribution of angular momentum is not such a good match, as the theory predicts far more low angular momentum gas than is seen. Once the baryon disk is self-gravitating, it is gravitationally unstable and fragments into stars. This general overview of disk formation can match many of the observed properties of disks provided that disk star formation is an inefficient process. Observed disks are still gas-rich and star formation extends over 50 or more disk dynamical time-scales.