Energy efficiency building retrofits in the United States and around the world are attractive investments, but receive far less attention and capital than they deserve. This is in part due to a narrow definition of their value, typically focused on energy cost savings alone, and in part due to confusion and uncertainty about how to calculate, present, and justify such value as part of a retrofit capital request. This guide addresses this confusion and uncertainty, providing practical guidance to enable real estate investors to incorporate all the benefits of efficiency retrofits into their decision making.