The initiation and growth of pits on iron and of crevices and pits on stainless steels in numerous electrolyte solutions, both under potentiostatic and under natural corrosion conditions, have been studied by scanning electron microscopy. The pit morphology on iron is controlled primarily by solution composition: in sulfate‐containing solutions the pits are initially crystallographic, but then become polished; in nonsulfate‐containing solutions they always remain crystallographic. On stainless steels the pit morphology is determined by solution composition and by the nature of the initiation site; it depends only secondarily on alloy composition. In stainless steels, both austenitic and ferritic, crevice corrosion is the prevalent corrosion form; pitting is initiated only at significantly higher potentials. The results are in agreement with an electrochemical study that showed that the potential across the interface in all local corrosion cells is in the active part of the anodic polarization curve of the metal and that pits and crevices propagate by the same mechanism.