A Premium Bond is a lottery bond issued by the United Kingdom government's National Savings and Investments agency. The bonds are entered in a regular prize draw and the government promises to buy them back, on request, for their original price. The bonds were introduced by Harold Macmillan in 1956. Investors can buy bonds at any time; they have to be held for a calendar month before they qualify for a prize. Numbers are entered in the draw each month, with an equal chance of winning, until the bond is cashed.