Self-determination is a cardinal principle of international law. But its meaning is often obscure. While the exact contours of the principle are disputed, international law clearly recognizes decolonization as a central application of self-determination. Most ordinary people also agree that the liberation of colonized peoples was a moral triumph. In the paper, I pursue a particular strategy for theorizing the principle: I start with a case where self-determination is widely considered appropriate—the case of decolonization—and try to get clear on precisely which values justified self-determination in that case. Specifically, I examine three philosophical theories of self-determination’s value: an instrumentalist theory, a democratic theory, and my own associative theory. I argue that our intuitions about decolonization can be fully justified only by invoking an interest on the part of alienated groups in redrawing political boundaries. This interest, I believe, may also justify self-determination in other cases, such as autonomy for indigenous peoples, and greater independence for Scotland or Quebec. Those who strongly support decolonization may have reason to endorse independence for these other minorities as well.