Third in the SPIE Field Guide Series, this is a summary of the methods for determining the requirements of an adaptive optics system, the performance of the system, and requirements for the components of the system. Many of the expressions are in the form of integrals. When that is the case, the authors show the results graphically for a variety of practical values. This volume is intended for students, researchers, and practicing engineers who want a "go to" book when the calculation is needed quickly.