This dissertation asks what it means to be faithful to the friend. From Aristotle onward friendship has often been taken as the foundation of political life, but as it is a private relation that excludes many fellow citizens, fidelity to the friend may conflict with the duties of citizenship and endanger the political realm. What is more, one can never be perfectly faithful to one’s friend, so is true friendship impossible? I argue that friendship, though always a risk, directs us toward a justice that is higher than the political. Moreover, friendship is a great good that is suited to our finitude. While our finitude renders perfect fidelity impossible, it is also the horizon within which alone friendship can take place. Friendship is possible for those who admit its impossibility, who love precisely that the other – whether the other person or a language – escapes them.Chapter 1 considers selected ancient and medieval examinations of friendship in order to clarify friendship’s unstable place in the borderlands of hostility and hospitality. Only the dispossession of the self opens it to alterity. Thus if friendship is possible, it is possible only between strangers, not citizens secure in their ipseity. To bind people into a community, it must also shatter open any community in which they believe themselves to be comfortably at home. Chapter 2 further explores, in light of Emmanuel Levinas’ ethics, the conflict between friendship and one’s obligation to others. Levinas posits a self who is absolutely responsible for every other according to an asymmetrical ethical relation; how then can one prefer the friend to others? I reply that friendship serves as a forceful reminder of the singularity of the other and of the inadequacy of the comparisons among people that politics must employ to determine whose interests will win out. Friendship is not, however, only a signpost that points to ethics: it is a good that needs no justification to be worthwhile. Chapter 3 proposes that friendship arises from our finitude. Drawing on Emmanuel Falque’s work, I maintain that finitude is a positive good that is suited to humans. Friends translate the world for each other – but what of the fact that translation is always unfaithful? It is impossible, as Jacques Derrida has emphasized, to maintain infinite fidelity to the friend, but this impossibility is constitutive of friendship. Stepping beyond this horizon would not lead to better friendships but would destroy the possibility of friendship by taking us outside the limits that constitute humanity, when it is as humans that we love each other in friendship. Chapter 4 further investigates the possibility of friendship by taking up the suggestion, raised in Marcel Proust’s In Search of Lost Time, that friendship is an illusion because it pretends to offer knowledge of another even though such knowledge is impossible. I argue that a careful reading of the Search reveals that writing itself functions as an act of friendship: the narrator discovers that through writing his world can encounter the worlds of others. True friendship is a relation across absence. Finally, chapter 5 shows how the promise of fidelity to the friend constitutes the self: the promise creates the very world that the self is called to translate for the friend. I conclude that although one can never achieve perfect fidelity to the friend, this is no reason to despair of fidelity: the very infidelity of the self’s witness to the friend may still bear witness to the friend’s irreplaceability. Bearing witness to the friend is a task to be undertaken in fear and trembling but also in gratitude and joy, for friendship is a great good of our existence within finitude.