Yang-Mills theory is a fundamental framework in theoretical physics that describes how certain types of force-carrying particles, known as gauge bosons, interact with matter. It generalizes the concept of electromagnetism to include other forces, such as the strong and weak nuclear forces, by using mathematical structures called gauge groups. The theory is named after physicists Chen-Ning Yang and Robert Mills, who developed it in the 1950s. It plays a crucial role in the Standard Model of particle physics, which explains how elementary particles and forces interact. Yang-Mills theory has significant implications for our understanding of the universe at the smallest scales.