This thesis discusses the development of a pulse tube cryocooler and the use of a software simulation tool called Sage in this effort. A pulse tube cryocooler is a type of refrigerator that operates in the cryogenic temperature range below 120 K (-153° C). The goal of this thesis spans from a basic understanding of the ideal thermodynamics of the pulse tube cryocooler (PTC) to a grasp of one commercial software package's ability to model an actual, non-ideal PTC. The history and theory are discussed leading to the state-of-the-art technology. The focus then turns to the specific development efforts of the author at his place of employment, Sunpower, Inc. The specific elements that led to the design of the Sunpower PTC are examined and the use of Sage simulation software is demonstrated. Finally, comparisons between experimental data and Sage predictions show the success of Sage as a simulation tool.