This chapter explains the main conceptions of sexual difference that have influenced feminist theory, tracing their roots in the psychoanalysis of Freud and Lacan, and then introducing the radical rethinking of sexual difference put forward by Luce Irigaray. For Irigaray, in the Western symbolic order there has only ever been sexual hierarchy, not genuine sexual difference. Her political program for changing the symbolic order to create a positive feminine subject-position—one that is not merely the underside or negative opposite of the masculine position—has been developed practically by some Italian feminists. Conceptions of sexual difference have also helped feminist theorists to rethink embodiment beyond the sex/gender distinction. The chapter concludes by considering how conceptions of sexual difference have made various current directions in feminist theory possible, including the new “material feminisms.”