This book develops the theory of typed feature structures, a new form of data structure that generalizes both the first-order terms of logic programs and feature-structures of unification-based grammars to include inheritance, typing, inequality, cycles and intensionality. It presents a synthesis of many existing ideas into a uniform framework, which serves as a logical foundation for grammars, logic programming and constraint-based reasoning systems. Throughout the text, a logical perspective is adopted that employs an attribute-value description language along with complete equational axiomatizations of the various systems of feature structures. Efficiency concerns are discussed and complexity and representability results are provided. The application of feature structures to phrase structure grammars is described and completeness results are shown for standard evaluation strategies. Definite clause logic programs are treated as a special case of phrase structure grammars. Constraint systems are introduced and an enumeration technique is given for solving arbitrary attribute-value logic constraints. This book with its innovative approach to data structures will be essential reading for researchers in computational linguistics, logic programming and knowledge representation. Its self-contained presentation makes it flexible enough to serve as both a research tool and a textbook.