This book demonstrates how to design an optical system using Synopsis CODE VR, a full-featured optical design program that has a command line interface. The complete design process (from lens definition to the description and evaluation of lens errors on to the improvement of lens performance) will be developed and illustrated using the program. This text is not a user’s manual for CODE V. Rather, it starts with a single lens to demonstrate the laws of optics and illustrates the basic optical errors (aberrations). Then, through a series of examples, demonstrations, and exercises, readers can follow each step in the design process using the CODE V commands to analyze and optimize the system for the lens to perform according to specifications. The text is organized to help readers (1) reproduce each step of the process including the plots for evaluating lens performance and (2) understand its significance in producing a final design.