To illustrate the importance of regulatory coordination to the PCAOB, more than 700 of the [audit] firms registered with the PCAOB are in countries outside the United States, although they may be affiliated with large, U.S. based audit firms. As required by the Sarbanes-Oxley Act, many of these firms are registered with the PCAOB because they audit non-U.S. companies whose securities trade in U.S. markets and are required to file audited financial statements with the SEC. In addition, as also provided for in the Act, a number of other non-U.S. firms are registered because they audit or wish to audit significant non-U.S. subsidiaries of multinational U.S. companies. With respect to both categories of firms, the PCAOB continues to work closely with its foreign counterparts to optimize efficiency in the oversight of these non-US firms.