This book argues that major patterns of variation across languages are structured by general principles of efficiency in language use and communication, an approach that has far-reaching theoretical consequences for issues such as ease of processing, language universals, complexity, and competing and cooperating principles. Hawkins argues that grammars are profoundly affected by the way humans process language. He develops a simple but elegant theory of performance and grammar by drawing on concepts and data from generative grammar, linguistic typology, experimental psycholinguistics and historical linguistics. In so doing, he also makes a laudable attempt to bridge the schism between the two research traditions in linguistics, the formal and the functional. Efficiency and Complexity in Grammars is a major contribution with far-reaching consequences and implications for many of the fundamental issues in linguistic theory. This is a tremendous piece of scholarship that no linguist can afford to neglect.