Companies produce financial statements that provide information about their financial position and performance. This information is used by a wide range of stakeholders (e.g., investors) in making economic decisions. Typically, those that own a company, the shareholders, are not those that manage it. Therefore, the owners of these companies (as well as other stakeholders, such as banks, suppliers and customers) take comfort from independent assurance that the financial statements fairly present, in all material respects, the company's financial position and performance.

To enhance the degree of confidence in the financial statements, a qualified external party (an auditor) is engaged to examine the financial statements, including related disclosures produced by management, to give their professional opinion on whether they fairly reflect, in all material respects, the company's financial performance over a given period(s) (an income statement) and financial position as of a particular date(s) (a balance sheet) in accordance with relevant GAAP. In many cases this is required by law.