This letter responds to your request for information on budget function classifications. Budget functions have long been used as supplementary presentations within budget and financial summaries of the federal government. Specifically in this letter, we discuss the origins and evolution of the current structure and recent spending trends by function. In addition, as agreed with your office, we also describe in this letter possible challenges in using these classifications as a framework for other governmentwide applications, such as the Federal Government Performance Plan, required by the Government Performance and Results Act, and the Statement of Net Cost in the Consolidated Financial Statements of the federal government. The budgetary information presented in this letter was developed from an automated system used by the Office of Management and Budget (0MB) to collect and process information for the President's annual budget submission. Although these data were not verified at the individual budget account level, we did summarize and reconcile fiscal year net outlays by subfunction to published sources. All growth rates and trend analyses are stated in constant dollars, using fiscal year 1996 as the base year. Appendix I provides additional details on our objectives, scope, and methodology.