In the last decade, the notion of competition has come to play a major role in syntactic theory, particularly in minimalist and optimality-theoretic syntax. On this view, a sentence can only be grammatical if it is "optimal'' in a set of competing candidates with respect to a given evaluation metric - economy in the minimalist program, quality of constraint profile in optimality theory. Preceded by a general introduction that outlines both common features and main differences among competition-based models, the ten articles in this book critically investigate the viability of competition in syntax from different points of view, concentrating on optimality theory and the associated concepts of constraint ranking and constraint violability.On the empirical side, the contributions focus on phenomena from a variety of languages where an account in terms of competition has some initial plausibility, among them word order, quantifier scope, chain realization, argument linking, Ersatzinfinitiv, Case assignment, and gapping. On the conceptual side, new light is shed on important issues concerning basic notions that are notoriously unclear (like the nature of the evaluation metric, the form of candidates and of candidate sets, the role of the input, and parallel vs. serial optimization). Furthermore, certain issues are addressed that are inherently problematic for optimality-theoretic syntax (like optionality, absolute ungrammaticality, gradient acceptability, and cumulativity of constraint violation).