This essay studies the way in which the sisters Ismene and Antigone and the dialogue that unfolds between them in Sophocles' Antigone have become central for twentieth-century feminist philosophy. It focuses on the dialogue that feminist philosophers have created with the play and its two female characters, seeking to turn Ismene and Antigone – and the play itself – into philosophical interlocutors. Examining how philosophical thinking attempts, by means of dialogue, to articulate the promises and failures embedded in relationships between sisters, it aims to articulate the connections between sisterhood and feminine being, meaning, and collective action. In particular, the essay centers on the way both Antigone and the relationship between Antigone and Ismene have been taken up as a theme in the philosophy of Luce Irigaray. Irigaray often turns to the vertical lines between mothers and daughters to study the fate of women under patriarchy, as well as the possibility of a future of a genuinely feminine order. Here, I focus on a few surprising passages where the category of "sister" is introduced by Irigaray and use it to think about the promise of horizontal links between women. More specifically, I probe the potential in relationships between women that are constituted by resemblance, rather than identity, and difference, rather than alterity, and do so by examining a specific attempt at a dialogue, the one that Luce Irigaray initiates with Simone de Beauvoir.