Understanding building performance is a central theme among building owners and managers. Measurement and verification (M&V) of savings from energy efficiency projects has evolved into a well-defined and mature discipline in North America. There are guidelines and protocols that define M&V, and a certification path is available for the professionals who practice it. The primary purpose of M&V is to validate that time, effort and money invested to reduce energy usage in buildings provides the expected results. This is done by accurately measuring (or estimating) the savings generated from any type of energy efficiency project, including major renovations, retrofits, facility improvements, and operational and behavioral changes. These projects can be implemented solely by a building owner or through outside parties, such as energy service providers, equipment manufacturers, financial service providers and utilities.