Businesses employ accounting firms to handle important financial tasks. Public companies must follow accounting rules set by the Securities and Exchange Commission (SEC) and following Generally Accepted Accounting Principles (GAAP). The SEC requires public companies to hire external accounting firms to audit their financial statements. Accounting firms specialize in other financial tasks, such as tax, management consulting, mergers and acquisitions and forensic accounting. The types of accounting firms required by a business depend on their accounting and business needs.