The passive region of stainless steels (SSs), as defined by the low current regime between the active-passive transition and the pitting potential or the transpassive potential, is discussed in terms of solid solution alloying and microstructure. In considering the beneficial effects of solid solution alloying, emphasis is placed on chromium, molybdenum, and nitrogen. The limitations of passive behavior resulting from carbides, sulfides, sigma, chi, delta ferrite, alpha prime, and alloying element depletion at precipitates are described. Enhanced passivity resulting from surface modification by high energy beams is discussed in terms of metallurgical changes at the surface. Links between the polarization curve and environmental cracking regimes are noted, as well as topics for future research.