Usually pictured in relations of opposition, political parties are sometimes inclined to make alliances. This article examines the ethical questions such arrangements give rise to. It considers first the formal characteristics of an alliance as a distinctive form of association, moving on to examine what reasons for alliance are good reasons. Intrinsic arguments that invoke epistemic or democratic criteria, and instrumental arguments that cite areas of shared programme or imperfect institutions, are weighed in turn, with the latter judged to be more consistent with the partisan ethos. The final section examines the normative standards to which alliances should be held once formed.