Enforced by the US Department of the Treasury (Internal Revenue Service and Financial Crimes Enforcement Network - FinCEN)

http://www.irs.gov/Businesses/Small-Businesses-&-Self-Employed/Bank-Secrecy-Act

The Currency and Foreign Transactions Reporting Act of 1970 commonly referred to as the “Bank Secrecy Act” or “BSA” requires U.S. financial institutions to assist U.S. government agencies to detect and prevent money laundering. The BSA is sometimes referred to as an “anti-money laundering” law (“AML”) or jointly as “BSA/AML.” Several AML acts, including provisions in Title III of the USA PATRIOT Act of 2001, have been enacted up to the present to amend the BSA.

Report of Cash Payments Over $10,000 Received in a Trade or Business (Form 8300): The general rule is that a business must file this report with the Internal Revenue Service if the business receives more than $10,000 in cash from one buyer as a result of a single transaction or two or more related transactions.

Report of Foreign Bank and Financial Accounts: If you own a foreign bank account, brokerage account, mutual fund, unit trust, or other financial account, then you may be required to report the account yearly to the Internal Revenue Service.

Currency Transaction Report (CTR) A CTR must be filed with FinCEN for each deposit, withdrawal, exchange of currency, or other payment or transfer, by, through or to a financial institution, which involves a transaction in currency of more than $10,000. Multiple currency transactions must be treated as a single transaction if they are conducted by or on behalf of the same person.

Suspicious Acticvity Report (SAR): Banks must file a SAR with FinCEN for any suspicious transaction relevant to a possible violation of law or regulation.

FAQs Regarding Reporting Cash Payments of Over $10,000 (Form 8300)
FAQs Regarding Report of Foreign Bank and Financial Accounts (FBAR)
BSA E-Filing System

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