The Japanese causative represents in a very pure form the problem of the morphology/syntax interface. Its three subtypes have attracted more attention and inspired more theoretical proposals than almost any other construction in the language. Analyses of the causative have had a major influence on many foundational aspects of syntactic theory, including control, case marking, clause structure, theta-theory and argument structure, and the morphology-syntax interface. In this paper, I focus on just one aspect of the causative puzzle: In what component of the grammar are the various causatives constructed? It turns out that the answers to many of the other syntactic questions posed by causatives depend on the theoretical choices made in answering this one. The paper opens with a review of the differing implications of lexicalist and non-lexicalist analyses for the architecture of a linguistic model, and then develops the arguments of Miyagawa 1994, 1998 for a unified, Late Insertion treatment of the ‘lexical’ and productive variants of the causative within the syntax. The domain of attachment of the causative morpheme is argued to determine whether its interpretation must be compositional or may be idiomatic, and whether it exhibits stem-conditioned allomorphy or not.