An auditor's report is a formal opinion, or disclaimer thereof, issued by either an internal auditor or an independent external auditor as a result of an internal or external audit, as an assurance service in order for the user to make decisions based on the results of the audit.

Auditor's reports are considered essential tools when reporting financial information to users, particularly in business. Many third-party users prefer, or even require financial information to be certified by an independent external auditor. Creditors and investors use audit reports from Supreme Audit Institutions (SAI) to make decisions on financial investments. Audit reports derive value from increasing the credibility of financial statements, which subsequently increases investors' reliance on them. In the government, legislative and anti-corruption entities use audit reports to keep track of the actions of public administrators on behalf of citizens. Therefore auditing reports are a check mechanism on behalf of the citizen, to ensure that public finances, resources and trust are managed in entities created to foster good governance, such as local authorities, government departments, ministries and related government bodies.