A system by which presidential candidates can tap into a pool of Treasury money to fund their campaigns. Candidates can use the funds, which come from a voluntary $3 check-off on individual tax returns, to pay for expenses in party primary elections if they meet certain fundraising threshholds and agree to a set of spending and other restrictions. Once a candidate becomes the official nominee of his or her party, he or she can elect to receive a flat grant of money to use for the remainder of the campaign. The system is administered by the Federal Election Commission.
While several presidential candidates in recent years have opted not to accept public financing (and the rules that go with it) for their primary campaigns, in 2008 Barack Obama became the first candidate to decline public financing in the general election since the system was enacted in 1971. His campaign raised far more money than he would have received from the government — more than $640 million versus $84.1 million.