The building envelope is one of the largest and most crucial systems that affect a building’s energy performance and its levels of occupant comfort. When the District of Columbia adopted new construction codes in early 2020, it included provisions (DCMR 12I, §126.96.36.199) that require building envelope system design review and testing. That requirement, called Building Envelope Commissioning (BECx), is a quality assurance process for verifying the owner’s requirements for the building enclosure are defined and met. As envelope systems become more and more complex alongside new requirements for increased building performance, building envelope commissioning will be a fundamentally important process to ensure quality. This resource intends to help owners, architects, other design professionals, and general contractors understand the District’s code requirements related to BECx and plan for incorporating the approach into the design and construction process within the District.