Thin-film coatings are ubiquitous on all optical components, such as lenses, mirrors, cameras and windows. Antireflection coatings are used on nearly all flat glasses, such as on windows, and architectural glasses. This chapter discusses the fundamental principles of designing thin films for optical coatings, specifically antireflection coatings, high-reflection coatings, and metal film optics. The reflection from several quarter-wave films can be calculated by simply extending the single quarter-wave film reflection calculations. The transfer matrix method is the most widely used technique for numerically modeling the optical effects of a number of parallel thin films stacked together. The design of metal film optics revolves around creating antireflection and high transmission coatings. Traditionally, physical vapor deposition techniques such as thermal evaporation and ion sputtering have been the primary methods used in the production of optical thin films. Chemical vapor deposition techniques are less popular for optical coatings due to the limited material inventory, requirement for precursors, and high process temperatures.