Why do supposedly accountability-enhancing electoral reforms often fail in young democracies? How can legislators serve their constituents when parties control the necessary resources? Unity through Particularism sheds light on these questions and more by explaining how parties can use personal vote-seeking incentives in order to decrease intra-party dissent. Studying a unique electoral reform in Mexico, the book provides a detailed description of how institutional incentives can conflict. It draws on a variety of rich, original data sources on legislative behavior and organization in 20 Mexican states to develop a novel explanation of how electoral reforms can amplify competing institutional incentives. In settings where legislative rules and candidate selection procedures favor parties, legislators may lack the resources necessary to build voter support. If this is the case, party leaders can condition access to these resources on loyalty to the party's political agenda.