Based on the authors’ experimental work over the last 25 years, presents basic concepts, state-of-the-art applications, and future trends in optical, atomic, and molecular physics. It provides all the background information on the main kinds of laser sources and techniques, offers a detailed account of the most recent results obtained for time- and frequency-domain applications of lasers, and develops the theoretical framework necessary for understanding the experimental applications. After a historical introduction, the book describes the basic concepts and mathematical tools required for studying the physics of oscillators. It then discusses microwave and optical resonators, crucial aspects of operation and fundamental properties of lasers, and precision spectroscopy and absolute frequency metrology. It also focuses on microwave and optical frequency standards and explores current and potential research directions. Accessible to scientists, postdoc researchers, and advanced undergraduate students, this self-contained book gives a wide-ranging, balanced overview of the areas—including frequency standards and clocks, ultra-high-precision spectroscopy, quantum information, and environmental metrology—revolutionized by the recent advent of optical frequency comb synthesizers (OFCSs) based on femtosecond mode-locked lasers. The book is also a useful guide to cutting-edge research for manufacturers of advanced laser systems and optical devices.