This book surveys the important concept of unification as it relates to linguistic theory and, in particular, to Functional Unification Grammar, Definite-Clause Grammars, Lexical-Function Grammar, Generalized Phrase Struture Grammar, and Head-Driven Phrase Structure Grammar. The notes include careful and correct definitions, as well as well-chosen examples of actual grammars, and a discussion of the relationships of computational systems and linguistic theories which use ideas from unification.