The Bona Fide Need Rule is a fundamental principle of appropriations law addressing the availability as to time of an agency's appropriation. 73 Comp. Gen. 77, 79 (1994); 64 Comp. Gen. 410, 414-15 (1985). The rule establishes that an appropriation is available for obligation only to fulfill a genuine or bona fide need of the period of availability for which it was made. 73 Comp. Gen. 77, 79 (1994). It applies to all Federal Government activities carried out with appropriated funds, including contract, grant, and cooperative agreement transactions. 73 Comp. Gen. 77, 78-79 (1994). An agency's compliance with the bona fide need rule is measured at the time the agency incurs an obligation, and depends on the purpose of the transaction and the nature of the obligation being entered into. 61 Comp. Gen. 184, 186 (1981) (bona fide need determination depends upon the facts and circumstances of the particular case). In the grant context, the obligation occurs at the time of award. 31 Comp. Gen. 608 (1952). See also 31 U.S.C. Sec. 1501(a)(5)(B). Simply put, this rule states that the Executive Branch may only use current funds for current needs – they cannot buy items which benefit future year appropriation periods (i.e., 1 October through 30 September) without a specific exemption. The net result of this rule is funds expire after the end date for which Congress has specified their availability. For example, a single year fund expires on 1 October of the year following their appropriation (i.e., FY07 appropriations. (for example, 1 October 2006 through 30 September 2007) expire on 1 October 2007).