This chapter intends to visit the subject of computer software as it applies to or contributes to the performance of energy audits in commercial buildings. A technically rigorous energy audit should include a significant amount of measurements of the actual operating parameters of the installed equipment. Only three issues must really be addressed when considering energy retrofit; technical feasibility, cost of installation and probable energy savings. While many practitioners perform their cost estimating by hand, the well-known estimating guides offer complete software programs to perform a wide range of estimating tasks. Many people would be slow to recognize that Computer Assisted Design and Drafting has a significant contribution to offer to the energy auditing process. While some practitioners still perform savings calculations the old-fashioned way, by hand, the majority of savings calculations are automated to at least a minimal extent at this time.