Attorney General's Report on the Use of Pen Registers and Trap and Trace Devices Under the Foreign Intelligence Surveillance Act [open pdf - 1MB]
This document was declassified (from Secret classification) on February 28, 2014, and includes the Attorney General's reports from years 2001-2013. From the 2001 report: "This report is submitted pursuant to the Foreign Intelligence Surveillance Act of 1978 (the 'Act'), [...] as amended, by Public Law No. 105-272, 112 Stat. 2404-2413 (1998), and covers all applications to use pen registers and trap and trace devices conducted under the Act during the period July 1, 2000 through December 31, 2000. The Government filed five applications with the Foreign Intelligence Surveillance Court (FISC) seeking authorization to use pen registers and/or trap and trace devices during this period. The Court authorized the use of the pen registers and/or trap and trace devices as requested in all five applications." Similar reports follow for years 2002-2013.
Office of the Director of National Intelligence: http://www.dni.gov/