This dissertation argues that we have no good reason to accept any one theory of properties as correct. To show this, I present three possible bases for theory-choice in the properties debate: coherence, explanatory adequacy, and explanatory value. Then I argue that none of these bases resolve the underdetermination of our choice between theories of properties. First, I argue considerations about coherence cannot resolve the underdetermination, because no traditional theory of properties is obviously incoherent. Second, I argue considerations of explanatory (...) adequacy cannot resolve the underdetermination, because every traditional theory of properties lacks the theoretical resources to adequately explain resemblance, causal powers, and predication. However, these inadequacies are easily remedied with theoretical modifications. But this results in an overabundance of modified, but adequate, theories of properties. Third, I argue explanatory virtues cannot resolve the underdetermination, because we have no reason to think explanatory virtues make theories of properties more likely to be true. I reject the common argument that explanatory virtues are truth-conducive in theories of properties because they are truth-conducive in scientific theories. Since none of the three bases for theory choice can resolve the underdetermination, I conclude that we have no good reason to accept any one theory of properties as correct. Finally, I consider the possibility of choosing one theory over the others on pragmatic grounds. But I argue that pragmatic grounds cannot resolve the underdetermination either. Instead, I suggest we accept the view I call 'instrumental pluralism,' which allows practitioners to use whatever theory of properties they find useful. Adviser: Jennifer McKitrick. (shrink)