Marcus Contextual Grammars is the first monograph to present a class of grammars introduced about three decades ago, based on the fundamental linguistic phenomenon of strings-contexts interplay (selection). Most of the theoretical results obtained so far about the many variants of contextual grammars are presented with emphasis on classes of questions with relevance for applications in the study of natural language syntax: generative powers, descriptive and computational complexity, automata recognition, semilinearity, structure of the generated strings, ambiguity, regulated...