This chapter explains the basic principles that govern light passing through a prism or a combination of prisms, and presents types of prisms and image formation. The concept of light passing through prisms is very important to photonics and has significant use in image formation and building optical devices. Prisms are widely used in building optical devices, such as a prism spectrometer, which is commonly used to study the wavelengths emitted by a light source. The most popular prisms are right angle prisms, Sir David Brewster’s angle dispersing prisms, Penta prisms, solid glass retro-reflectors, equilateral dispersing prisms, littrow dispersion prisms, wedge prisms, roof prisms, and Dove prisms. Dove prisms are commonly used as image rotators. A prism design useful in spectrometers is one that produces a constant deviation for all wavelengths as they are observed or detected. Prism combinations are commonly used in optical instruments for purposes such as inversion of an image in prism binoculars.