They are backed by the full faith and credit of the U.S. government.
Treasury bills are low-risk investments with a broad and liquid secondary market.
The interest earned on Treasury securities is exempt from state and local taxes. However, because T-bills are free of default risk, T bills generally have lower yields than corporate issues of comparable maturities. The reason for this is that T-bills are free of default risk. The investor pays less than face value for the T-Bills and they are redeemed at maturity at face value. The difference between the purchase price and the face value of the T-bill is the investor's return.