Taking its starting point in an ancient understanding of hospitality and guest friendship, the paper offers a philosophical interpretation of the ethical dimension of alliances. Entering into an alliance presupposes certain ethical dispositions, first of all trust, which allies develop over time by offering each other testimonies of trustworthiness and by keeping promises. Insofar as the alliance is developed further in order to last, the allies will have to adjust to changes, prevent conflict and solve problems together which imply, above all, joint critical thinking. The paper argues that friendship can serve as an analogue for good alliances, in which the parties involved do not only think about furthering their own projects, but they take into account and question possible flaws and future consequences, also for others outside the alliance.