The United States national debt represents the total financial obligations of the federal government, meticulously tracked by the U.S. Treasury's Bureau of the Public Debt. This crucial economic indicator consists of two major components: public debt (approximately 74%) and intragovernmental holdings (about 26%). Public debt includes Treasury securities—bills, notes, and bonds—held by individuals, corporations, state/local governments, Federal Reserve banks, and foreign investors, with China and Japan historically being the largest foreign holders. Intragovernmental holdings represent debt the government owes to itself, primarily through federal trust funds like Social Security, Medicare, and federal employee retirement funds. The debt ceiling, established by Congress in 1917, sets the maximum amount of debt the Treasury can issue. The debt-to-GDP ratio, a key metric for assessing fiscal sustainability, has fluctuated significantly throughout U.S. history, with notable increases during major events like World Wars, the 2008 financial crisis, and the COVID-19 pandemic.