The Retro-Commissioning (RCx) process includes preliminary assessment, investigation, energy modeling and estimating rates of return on retrofits, developing a Master List of Findings, conducting retrofits based on estimated rates of return, and verification testing to verify economic results. This presentation will address the typical approach to performance verification testing, how it is planned and conducted, what the roles are of the professionals involved in the RCx process, what systems typically require verification testing, and what are the building owner's responsibilities are for on-going continuous RCx. Typical methods of performance verification testing for building enclosure, mechanical, electrical, plumbing, fire protection, components and systems will be discussed. Representative project histories will be presented.