The OMB A-133 Compliance Supplement is a large and extensive United States federal government guide created by the Office of Management and Budget (OMB) and used in auditing federal assistance and federal grant programs, as well as their respective recipients. It is considered to be the most important tool of an auditor for a Single Audit.
It was created following amendments in 1996 to the Single Audit Act based on numerous studies performed by the Government Accountability Office, the President's Council on Integrity and Efficiency and the National State Auditors Association (NSAA). It serves to identify existing important compliance requirements that the Federal Government expects to be considered as part of a Single Audit. Without it, auditors would need to research many laws and regulations for each single program of a recipient to determine which compliance requirements are important to the Federal Government. For Single Audits, the Supplement replaces any agency audit guides and other audit requirement documents for individual Federal programs.[1]