This chapter uses building performance evaluation (BPE) to designate the general activity of building performance evaluation and post-occupancy evaluation (POE) for BPE undertaken in the first two or three years after a building's occupation, where the findings can influence those who commissioned and undertook the design and building work. However, one aspect of building performance energy use began to receive much attention, leading to developments in regulation, energy management, and new techniques and technologies. Partners in Technology (PiT) supported some multi disciplinary work on building performance, including Probe Post-occupancy review of buildings and their engineering which undertook and published 20 POEs of recently completed buildings between 1995 and 2002. The UK government also put its faith in PFI, the Private Finance Initiative, where a contractor finances, designs, builds and operates public assets. Usable Buildings Trust (UBT) has concluded that society needs new institutions to develop and properly represent the knowledge domain of building performance in use.