The origin of savings bonds and the periods of their greatest use historically are associated with wartime economies. At such times, savings bonds serve two functions: by drawing income off into savings and away from day-to-day spending, they keep the combination of too much money and too few goods from driving prices up, and they provide the government money to pay for the war. Generally, a savings bond is a written promise by the government to repay, with interest at a given rate and specified time, a sum of money being lent to it by an individual.