We survey modern models of delegation which assume that a boss and subordinate pursue their own goals. Among the major themes covered are the following: the conditions under which the boss will prefer to delegate versus those in which she will prefer to retain authority; the ways in which a boss can induce a subordinate to truthfully reveal information; when rational principals will use the ally principle (i.e., delegate to agents with similar goals); delegation in repeated interactions; and the ways in which delegation can overcome commitment problems. These ideas are applied to a wide variety of institutions, including intra-legislative organization, executive-legislative relations, and central banks.