The Democratic and Republican parties select their presidential nominees through a complex, fundamentally unstable process. It is an awkward amalgamation of disparate components, each designed to empower different constituencies within the party and pursue different goals. Each party ultimately chooses its nominee at a national convention comprised of delegates from each state. The mechanisms for selecting delegates to the national convention, however, are distinct from the procedures for determining the presidential candidates for whom those delegates must vote. National convention delegates are often selected at statewide or congressional-district conventions or through other intraparty mechanisms. They are typically pledged or “bound” to presidential candidates based on the outcomes of presidential preference contests, such as primaries and caucuses. Because of the complicated relationship among these components, the national convention need not nominate the person who received the most primary and caucus votes nationwide, won the most delegates, or prevailed in the most primaries and caucuses.