Also known as T-Bills and are securities that have been issued by the Treasury Department of the United States, treasury bills have the backing of the United States government behind them, so they are usually safe investments. Unlike other types of securities, treasury bills will mature in a year or less. This means a person can invest without having his or her money tied up for an exceptionally large period of time. These securities do no pay interest before their maturity date, but many people see treasury bills as one of the safest investments that a person can make in the United States. These bills can be purchased with different maturity dates ranging from 28 days, 91 days, 26 weeks or one year. The minimal amount that can be spent on treasury bills was at one point a 1,000 dollars but has since dropped to 100 dollars.