This guide provides guidance and resources to auditors assigned to assess existing energy savings performance contract (ESPC) projects. It describes resources, documents, and processes related to ESPC projects. It also describes the U.S. Department of Energy's ESPC indefinite delivery, indefinite quantity (IDIQ) contract timeline of key resources for reference when determining applicable guidance and presents common findings from past audits of ESPC projects with specific references to the DOE ESPC IDIQ contracts and supporting documents.