Possible worlds theory is one of the most important developments in analytic philosophy within the last fifty years. Possible worlds have been put to use in almost every problem in metaphysics, been used to clarify important epistemic ideas such as luck and reliability, helped us understand mental content, and been a crucial tool in philosophy of religion. An essential part of possible worlds theory is what I call Orthodox Modal Semantics (OMS). In my dissertation I argue that an alternative theory, Unorthodox Modal Semantics (UMS), should be adopted. We should accept UMS because it is useful. Specifically, it helps us solve important problems involving counterfactuals, modal epistemology, free will, and meta-philosophy. In the first chapter I present the argument for acceptance of UMS based on its utility. Specifically, we should prefer UMS to other modal semantics because it can be used to solve three important problems. In the second chapter I present UMS and compare it to OMS. There are two primary differences between the theories. UMS evaluates modal claims not with respect to possible worlds but with respect to less than maximal states of affairs. Second, UMS introduces the concepts of explicit and implicit truth at a state of affairs while OMS relies merely on truth at a state of affairs. In chapters 3--5 I apply UMS to various problems. Each of these chapters defends one premise in the argument from utility presented in chapter 1. In Chapter 3 I address The Problem of Modal Knowledge. I argue in chapter 4 that by applying UMS we can both accept the conclusions of metaphysicians and reject the claim that worlds with bizarre arrangements of stuff are possible. Chapter 5 contains an application of UMS to the evaluation of counterfactuals with impossible antecedents. Finally, I end the dissertation by ruling out a competitor to UMS, the Theory of Impossible Worlds.