When a reasonable agent deliberates about what to do, she entertains only a limited range of possible courses of action. A theory of practical reasoning must therefore include an account of deliberative attention: an account that both explains the patterns of deliberative attention that reasonable agents typically display and allows us to see why these patterns of deliberative attention are reasonable. I offer such an account, built around two, central claims. (i) A reasonable agent who cares about some end is disposed to exclude courses of action which she believes to be incompatible with that end from the range of possibilities that she will entertain as options in practical deliberation. As I shall put it, an agent’s cares establish deliberative boundaries for her practical thought. (ii) The stability of a deliberative boundary varies with the depth of the care that explains it. These two claims motivate the Boundary-Driven Model of the path that a reasonable agent’s deliberative attention will take in temporally extended deliberation. If we locate the model within a maximizing conception of practical rationality, then boundary-driven deliberation, of the sort that the model describes, can be understood and justified instrumentally, as a heuristic device. But if we suppose that there is no single index of value that successful practical choice maximizes, then boundary-driven deliberation is partly constitutive of reasonableness in practical thought. It allows an agent facing plural and incommensurable values to frame her deliberative problems narrowly enough that, in conjunction with deliberative devices which are not part of the model but which are compatible with it, she may be able to reach a non-arbitrary decision – and so give a determinate, verdictive sense to the phrase “the best course of action available to me” in cases in which a determinate meaning for this phrase would otherwise be lacking.