Gauge theory is a mathematical and conceptual framework in physics that describes the fundamental forces of nature by requiring that the underlying physical laws remain unchanged (invariant) under local symmetry transformations. These local symmetries necessitate the existence of mediating force particles, known as gauge bosons, which transmit interactions between matter fields. The theory dictates the structure of these interactions, defining how different types of matter particles couple to the forces. It provides the foundational structure for modern particle physics models, providing a highly unified description of the electromagnetic, weak, and strong nuclear forces.