Langmuir Theory, developed by Irving Langmuir in the early 20th century, describes the adsorption of molecules onto solid surfaces. It explains how gas molecules adhere to a surface until a maximum coverage is reached, forming a monolayer. The theory assumes that adsorption occurs at specific sites and that each site can hold only one molecule. The model is based on several key assumptions, including that the adsorption process is reversible and that the energy of adsorption is constant. Langmuir Theory is widely used in fields like catalysis, surface chemistry, and material science to understand and predict how substances interact with surfaces.