A long-standing, near-universal, and erroneous practice of teaching syntax in a void exists, as if the communicative function of language had nothing to do with syntax. And semantics has customarily been taught in sequence after syntax, or else not at all. Based upon graduate courses taught at Stanford University, this work seeks to redress this situation by building up syntactic and semantic aspects of grammatical theory in an integrated way from the start, under the assumption that neither is of linguistic interest divorced from the other. The particular theory presented, head-driven phrase structure grammar (HPSG) – so-called because of its central notion of the grammatical head – is an information-based (or 'unification-based' theory that has its roots in a number of different research programs within linguistics and neighboring disciplines such as philosophy and computer science. Thus HPSG draws upon and attempts to synthesize insights and perspectives from several families of contemporary syntactic theories, such as categorial grammar, lexical-functional grammar, generalized phrase structure grammar, and government-binding theory; but many of its key ideas arise from semantic theories like situation semantics and discourse representation theory, and from computational work in such areas as knowledge representation, data type theory, and formalisms based upon the unification of partial information.