U(1) Gauge Theory is a fundamental concept in theoretical physics that describes how certain forces, like electromagnetism, operate. It is based on the idea of symmetry, specifically the U(1) symmetry group, which represents the phase transformations of complex numbers. This theory helps explain how particles interact with electromagnetic fields through the exchange of virtual particles called photons. In U(1) Gauge Theory, the principle of gauge invariance ensures that the laws of physics remain unchanged under local transformations. This leads to the introduction of a gauge field, which mediates the interactions between charged particles, such as electrons. The theory is a cornerstone of the Standard Model of particle physics, providing a framework for understanding electromagnetic interactions.