Optimality theory has rapidly become the dominant framework in formal phonological theory. OT fundamentally revises the basic notions of generative grammar, replacing rules and derivations with a system of interacting constraints. Early work in OT tended to concentrate mainly on prosodic phonology and the phonology-morphology interface, and it was not initially clear how the theory could attack the rich range of phenomena now found in segmental alterations. However, there is now a body of work that concentrates on working out the details of featural phonology with OT, and this work shows that the theory allows superior explanations of the typological possibilities and the underlying motivations for these phenomena. This volume brings together current work by some of the influential researchers in this area, ranging from the authors of recent influential dissertations to prominent senior faculty.