Henry Smith here develops a theory of syntactic case and examines its synchronic and diachronic consequences. Within a unification-based framework, the book draws out pervasive patterns in the relationship between morphosyntax 'linking' and grammatical function. Beginning with a detailed study of dative substitution in Icelandic, the author moves on to examine a wide array of synchronic and diachronic data and to construct a typology of case.