This essay argues against two presumptions: first, that the psychoanalytic approach to sexuality is ahistorical; and second, that critics cannot speak of heterosexuality before its 19th‐century invention. Looking to Lacanian psychoanalysis, and particularly to Lacan’s theory of sexuation (or sexual difference), this essay develops a queer history of heterosexuality premised on the idea that ‘heterosexuality’ is simply the latest way of describing a structural relation between the sexes. Lacan calls this structure ‘the sexual relation’, and describes it as a fantasy that man and woman are two halves of the same whole. At the same time, he insists that ‘the sexual relation does not exist’: that neither sex can actually make the other whole. Lacan’s own reading of Shakespeare’s Hamlet– focused in part on Hamlet’s antagonism toward Ophelia following the prince’s discovery of his father’s ‘castration’– offers an example of how to queer heterosexuality in pre‐19th‐century texts. My reading of Measure for Measure offers a second example, one that likewise evokes Freud’s mytho‐historical account of the murder of the primordial father and the subsequent creation of a disinterested ‘law’ in the father’s name (Lacan’s Name of the Father). This essay concludes by suggesting that the fantasy of the sexual relation falters in both plays on the ‘obscene’ revelation of the law’s/the Father’s sinfulness.