United States Treasury securities are government debt instruments issued by the United States Department of the Treasury to finance government spending as an alternative to taxation. Treasury securities are often referred to simply as Treasurys. Since 2012, U.S. government debt has been managed by the Bureau of the Fiscal Service, succeeding the Bureau of the Public Debt.

There are four types of marketable treasury securities: Treasury bills, Treasury notes, Treasury bonds, and Treasury Inflation Protected Securities (TIPS). The government sells these securities in auctions conducted by the Federal Reserve Bank of New York, after which they can be traded in secondary markets. Non-marketable securities include savings bonds, issued to the public and transferable only as gifts; the State and Local Government Series (SLGS), purchaseable only with the proceeds of state and municipal bond sales; and the Government Account Series, purchased by units of the federal government.

Treasury securities are backed by the full faith and credit of the United States, meaning that the government promises to raise money by any legally available means to repay them. Although the United States is a sovereign power and may default without recourse, its strong record of repayment has given Treasury securities a reputation as one of the world's lowest-risk investments.