Non-marketable debt securities issued by the U.S. Treasury Department that are backed by the full faith and credit of the federal government. They are considered low risk, and the interest income is generally not subject to state or local taxes. There are currently three types of U.S. savings bonds: Series “EE”; Series “I”; and Series “HH.” Series EE bonds currently have a maturity of 17 years, and are sold at 50% of their face value, which range from $50 to $10,000. Series I bonds are indexed for inflation, and are sold at face value in denominations of $50, $75, $100, $200, $500, $1,000, $5,000, and $10,000. Series HH bonds have maturities of 20 years, provide interest income every six months, and are issued in denominations of $500, $1,000, $5,000, and $10,000. Series HH bonds cannot be purchased with cash, but may be acquired in exchange for matured bonds of the same series or for Series EE bonds.