The United States accounting and professional services landscape is dominated by the elite "Big Four" certified public accounting firms—Deloitte, PricewaterhouseCoopers (PwC), Ernst & Young (EY), and KPMG—which audit the vast majority of publicly traded corporations. Below this top tier, prominent national mid-tier CPA and advisory powerhouses like RSM US, BDO USA, Grant Thornton, and Crowe handle complex tax, audit, and financial consulting for large commercial enterprises.