A quantitative theory is presented for calculating the folding of a polymer, especially as applied to the renaturation of globular proteins. The theory applies to both thermodynamically and kinetically determined processes, so that not only can the equilibrium result be calculated but also the time course of folding. Since it is not automatically assumed that the folding will result in a single "native" conformation, it is possible to conclude that the polymer will exist as a random coil under appropriate conditions. A Monte Carlo method for applications is discussed in detail, and a very simple example is presented.