The British middle class considered friendship between women a crucial element of conventional femininity, yet friendship is oddly absent from recent studies of domestic ideology and family history. This lacuna is all the more striking given the attention to women’s friendships in conduct manuals and in lifewriting, a term that comprises diaries, letters, autobiographies and biographies. This essay uses those documents to distinguish between non-sexual friendships and other types of relationships that 20th-century feminist and lesbian theorists have often mistakenly conflated with friendship. After providing a basis for distinguishing friendship from 1) unrequited love, 2) infatuation, and 3) long-term sexual partnerships between women modeled on marriage, the article analyzes the repertory and significance of friendship itself. Friendship played a double role in Victorian women’s lives: it reinforced ideal qualities attributed to women, such as altruism and fidelity, but it also allowed women to engage in the kinds of competition, agency, and sensual indulgence that were normatively assigned to men. That double quality constitutes the “play of the system”, the elasticity that results when a social relationship allows actors to modify rules without essentially changing them.