Microlenses and microlens arrays are a vital part of modern optical systems with applications in MEMS and sensor systems. This book explores the physics and optical properties of a range of microlenses, along with their fabrication, tuning, and applications in various fields. Although focusing on liquid lenses, the text covers all lens systems. The authors discuss such topics as microfabrication and nanofabrication, liquid interfaces, surface tension, variable focus, and lab on chips. They also provide a discussion of the challenges posed by current microlenses.