The dielectric microstructures act as ultrahigh Q factors optical cavities, which modify the spontaneous emission rates and alter the spatial distributions of the input and output radiation. The editors have selected leading scientists who have made seminal contributions in different aspects of optical processes in microcavities. Every attempt has been made to unify the underlying physics pertaining to microcavities of various shapes. This book begins with a chapter on the role of microcavity modes with additional chapters on how these microcavity modes affect the spontaneous and stimulated emission rates, enhance nonlinear optical processes, used in cavity-QED and chemical physics experiments, aid in single-molecule detection, influence the design of microdisk semiconductor lasers, and how deformed cavities can be treated with classical chaos theory.