Obligations incurred by the Treasury subject to the statutory limit set by Congress. Until World War 1, a specific amount of debt was authorized for each separate security issue. Beginning with the Second Liberty Loan Act of 1917, the nature of the limitation was modified until, in 1941, it developed into an overall limit on the outstanding Federal debt. As of March 1999, the debt limit was $5,950,000 million; the limit may change from year to year. The debt subject to limitation includes most of the Treasury's public debt except securities issued to the Federal Financing Bank, upon which there is a limitation of $15 billion, and certain categories of older debt (totaling approximately $595 million as of February 1991).