A Treasury bill (or T-bill) is a short-term debt security issued by the US Treasury with a maturity period ranging from four weeks to one year. T-bills are purchased at a discount rate to their face value, which is paid out in full when the T-bill reaches maturity. For example, a $1,000 T-bill might cost $950 to purchase, generating a $50 return. T-bills generally rise in value and approach par value as the maturity date nears.