A liberty bond or liberty loan was a war bond that was sold in the United States to support the Allied cause in World War I. Subscribing to the bonds became a symbol of patriotic duty in the United States and introduced the idea of financial securities to many citizens for the first time.

War bonds are debt securities issued by a government to finance military operations and other expenditure in times of war without raising taxes to an unpopular level. They are also a means to control inflation by removing money from circulation in a stimulated wartime economy. War bonds are either retail bonds marketed directly to the public or wholesale bonds traded on a stock market. Exhortations to buy war bonds have often been accompanied by appeals to patriotism and conscience. Retail war bonds, like other retail bonds, tend to have a yield which is below that offered by the market and are often made available in a wide range of denominations to make them affordable for all citizens.