Electromagnetic theory is a fundamental branch of physics that describes the interactions between electric and magnetic fields and how they give rise to electromagnetic waves. The theory provides the foundation for understanding a wide range of physical phenomena, including the behavior of light, radio waves, and other forms of electromagnetic radiation. Electromagnetic theory is essential not only in classical physics but also in modern technological applications, such as communication systems, medical imaging, and radar.

The development of electromagnetic theory is rooted in the pioneering work of James Clerk Maxwell, who formulated a set of equations known as Maxwell's equations in the 19th century. These equations describe how electric and magnetic fields are generated and altered by each other and by charges and currents. Maxwell's equations unify the concepts of electricity and magnetism into a single framework, revealing that light itself is an electromagnetic wave propagating through space. This groundbreaking discovery led to the realization that visible light, radio waves, microwaves, infrared radiation, ultraviolet light, X-rays, and gamma rays are all part of the electromagnetic spectrum, differing only in their frequency and wavelength.