Audit reports are generally used when the most assurance among these 3 levels of Financial Statement Reporting is desired.  This level of assurance is common when there is substantial amount of debt (and may be required by the lending institution), when there is an off-site owner, and when the Company, owner and/or management desire the results of such testing and reporting to substantiate the notion that the books and records are substantially correct.  In many cases, the Audit involves specific testing of transactions, communications with attorneys and verifications of balances with third parties.  

The Financial Statement Audit Report may include several paragraphs, including: We conducted our audit in accordance with auditing standards generally accepted in the United States of America .  Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement.  An audit includes examining, on a test basis, evidence supporting the amounts and disclosures in the financial statements.  An audit also includes assessing the accounting principles used and significant estimates made by management, as well as evaluating the overall financial statement presentation.  We believe that our audit provides a reasonable basis for our opinion.