  We present a scaling description of a metal-insulator transition in
two-dimensional electron systems that is driven by a vanishing compressibility
rather than a vanishing diffusion coefficient. A small set of basic assumptions
leads to a consistent theoretical framework that is compatible with existing
transport and compressibility measurements, and allows to make predictions for
other observables. We also discuss connections between these ideas and other
theories of transitions to an incompressible quantum fluid.
