The Big Four are the four largest global accounting firms—Deloitte, Ernst & Young (EY), PricewaterhouseCoopers (PwC), and Klynveld Peat Marwick Goerdeler (KPMG), as measured by revenue. Aside from auditing services, the Big Four offer tax, strategy and management consulting, valuation, market research, assurance, and legal advisory services. They are the leading source of tax law interpretation and experts on changes in accounting and auditing standards.