We have used electron microscopy to examine the surfaces of lysozyme crystals and deduce mechanisms of crystal growth. We find that growth occurs by a lattice defect mechanism at low supersaturation and by two-dimensional nucleation at high supersaturation. Step velocities and two-dimensional nucleation rates are obtained, and their dependence on supersaturation is compared with theory. Some features of the observed surface structure can be related to the specific topology and strengths of the bonds in the P4(3)2(1)2 lattice. Preliminary results on the early stages of nucleation and the phenomenon of cessation of growth are presented.