Treasury bills (T-Bills) are a type of debt security issued by the U.S. Department of Treasury. T-bills are short-term securities, with maturities of one year or less. They are considered to be among the safest investments, as they are issued by the U.S. government and are backed by its full faith and credit. T-bills are sold at a discount from their face value, and the difference between the purchase price and the face value represents the interest earned. They are often used as a benchmark for short-term interest rates.