The Supreme Court’s decision in Citizens United v. FEC is widely considered a major roadblock for campaign finance reform, and particularly for limiting third party spending in federal elections. In response to the decision, commentators, scholars, and activists have outlined a wide range of legislative and regulatory proposals to limit the influence of third party spending, including constitutional amendments, public financing programs, and expanded disclosure rules. To date, however, they have not considered the possibility that third party spending can be restrained by a self-enforcing private contract between the opposing campaigns. This Essay argues that private ordering, rather than public action, is an additional approach for limiting third party campaign spending. It explains the design of a contract between opposing campaigns that is self-enforcing and restricts third party spending; identifies the conditions under which such a contract is likely to be offered and accepted; shows how political dynamics push third parties and campaigns to adhere to the contract’s spending restrictions; and discusses possible loopholes and challenges. While private ordering through a self-enforcing contract might seem like wishful thinking, precisely this kind of contract, “The People’s Pledge,” succeeded in keeping out third party spending on television, radio, and internet advertising in the most expensive Senate race in history, the 2012 Brown-Warren race in Massachusetts. Since then, this kind of contract has been adopted in two other federal congressional races and debated and offered in a wide range of other races. In the context of political gridlock in Congress, the emergence of a private ordering option to achieve campaign finance reform goals is significant. This Essay analyzes the conditions under which private ordering, rather than public law reform, can limit third party spending in elections. It draws on examples, particularly that of the original “People’s Pledge,” to illustrate the general parameters of these contracts, and it considers the implications of these contracts for election law and policy.