Private, self-regulatory organization overseen by the US Securities & Exchange Commission.

http://pcaobus.org/Pages/default.aspx

The Public Company Accounting Oversight Board (or PCAOB) is a nonprofit corporation established by Congress to oversee the audits of public companies in order to protect the interests of investors and further the public interest in the preparation of informative, accurate and independent audit reports. The PCAOB also oversees the audits of broker-dealers, including compliance reports filed pursuant to federal securities laws, to promote investor protection.

The PCAOB has the power to: register public accounting firms that prepare audit reports for issuers; set auditing, quality control, ethics, independence and other standards relating to the preparation of audit reports by issuers; conduct inspections of registered public accounting firms; and conduct investigations and disciplinary proceedings concerning and impose appropriate sanctions where justified upon, registered public accounting firms and associated persons of such firms (including fines of up to $100,000 against individual auditors, and $2 million against audit firms). Replaced the Public Oversight Board, a private organization whose members were appointed by the auditing industry.

PCAOB Rules

US and non-US accounting firms that prepare, issue, or participate in audit reports of issuers, brokers, and dealers.

http://en.wikipedia.org/wiki/Public_Company_Accounting_Oversight_Board