Kenneth Waltz’s name is irrevocably associated with the term structure. Waltz’s theory of international politics, as expounded in the 1970s, is a systemic theory and, for that reason, a structural theory (1975: 45; 1979: 40). His systemic perspective quickly came to be known as structural realism, and Waltz (2000) has himself adopted this label. In an act of sublime flattery, one of Waltz’s most strident critics, Alexander Wendt, went so far as to describe constructivism in the field of International Relations “as a kind of ‘structural idealism’” (1999: 1; also see p. xiii). In this essay, I suggest that Waltz’s theory also bears describing as a kind of structural idealism, though hardly the kind that Wendt has espoused. Appropriately developed, Waltz’s conception of structure suits, even supports, a strong version of constructivist social theory.