Environmentally induced subcritical crack growth occurs in most metallic ma terials given the appropriate material, environment, and stress conditions. Much is known about the conditions which cause stress corrosion cracking (SCC) in metallic materials, but much less is known about the processes which control environment-induced crack initiation and propagation. There is presently no description of the flaw length, flaw shape, and local chemistry conditions that coincide with the transition from a localized corrosion phenomenon and the initiation of a crack. Although there have been considerable attempts to describe the rate-limiting steps in crack propagation, a number of issues are unresolved, including specifics about the crack-tip conditions, crack length effects, processes controlling the Stage I SCC region, and details about the crack advance processes in both transgranular stress corrosion cracking (TGSCC) and intergranular stress corrosion cracking (IGSCC). A summary of these unresolved issues and some analysis of their effect on SCC is given in this paper.