Over the centuries, scientists have devised several ideas to explain the origins of the laws of nature. As we better understood the individual theories, researchers realized that a lot of phenomena can be explained as arising from a deeper cause, like how electricity, magnetism, chemistry, and light all can arise from electromagnetism. In the modern day, we know of two theories that describe nearly all experiments. The theory that describes the subatomic world is called the standard model of particle physics, while the theory that describes the cosmos is called general relativity. This chapter describes how these theories came to be devised and the range of phenomena they successfully describe.