The one-atom maser or micromaser is a quantum optics system that allows the observation of single two-level atoms interacting with a single-mode field. The microscopic nature of the micromaser system and the absence of significant amounts of stochasticity and noise, allows for the observation of behavior that is drastically different from that of macroscopic masers. This dissertation describes theoretical studies of the micromaser system and extensions of the previous micromaser theory to improve its agreement with experimental observations.