Law has different meanings as well as different functions. Philosophers have considered issues of justice and law for centuries, and several different approaches, or schools of legal thought, have emerged. In this chapter, we will look at those different meanings and approaches and will consider how social and political dynamics interact with the ideas that animate the various schools of legal thought. We will also look at typical sources of “positive law” in the United States and how some of those sources have priority over others, and we will set out some basic differences between the US legal system and other legal systems.