According to the U.S. Department of Energy, buildings consume 40 percent of all the energy used nationwide. Achieving optimal energy efficiency in buildings can drastically reduce overall energy consumption, and windows can play a key role in achieving improved performance. Building energy codes, standards and voluntary practices exist to provide a target for achieving recognized and acceptable levels of energy efficiency and establish minimum performance standards for residential and commercial buildings. In order to meet codes and standards, windows must be tested, rated, and designed for optimal performance. This course will provide a thorough introduction to the relationship between windows and energy efficiency and the importance of installing appropriate windows with high performance technologies. We will discuss window performance ratings and how they can help to reduce energy costs and improve the comfort of building occupants.