The law requires each “United States person” who has a financial interest in or signature authority over any foreign financial account to file an FBAR if the aggregate value of the foreign financial accounts exceeds $10,000 at any time during the calendar year. The form required is FinCEN Form 114.
This is one that should be pretty well known by now. The obligation to file a Report of Foreign Bank and Financial Accounts (FBAR) with the US Treasury was initially imposed by the Bank Secrecy Act in 1970. Here are the Instructions to FinCEN Form 114 (FBAR). You can electronically file Form 114 for free here.
What Is a Financial Interest for the FBAR?