Post-occupancy evaluation (POE) is an assessment of a physically defined space after people have occupied it. This last phase of the design cycle advances a series of questions: Did the ideas and recommendations put forward in the programming phase of the design process work? Have occupants’ goals and intentions been achieved? Which specific behavioral responses to the structure have occupants shown? Beyond defining different types of post-occupancy evaluations, and including a brief history of the practice, this chapter explains several methods for studying attitudes and behaviors in a setting, and the physical setting itself. Standardized methods (observation, interviews, surveys) and behavioral mapping techniques are detailed, along with a discussion of the importance of usability, controllability, and comfort to occupant satisfaction and, often, to building performance. A case study about the usability of lighting and heating, ventilation, and air conditioning retrofits in three buildings is also included to provide an applied example of POE in an existing building setting.