Treasury Securities
Treasury securities—including Treasury bills, notes, and bonds—are debt obligations issued by the U.S. Department of the Treasury. Treasury securities are considered one of the safest investments because they are backed by the full faith and credit of the U.S. government. The income from Treasury securities is exempt from state and local taxes, but not from federal taxes.
For more information about Treasury securities, visit the website of the U.S. Department of the Treasury’s Bureau of the Public Debt. You can learn about "Savings Bonds" in our Fast Answers databank.
http://www.sec.gov/answers/treasuries.htm