The literature on legislatures suggests a series of social choice, collective action, and individual decision-making problems that ambitious politicians face when making voting choices in legislatures. The most influential modern theories based on the US Congress focus on how politicians delegate power to central institutions that constrain legislative choices in order to solve these problems. In many contexts, however, legislators do not have incentives to delegate such authority. Using the case of the Colombian Congress, this dissertation is focused on exploring how legislators can also achieve their goals and policy ends using non-hierarchical forms of organization. Specifically, voting choices are constrained through a process of self-organization. This process happens without a central authority and is based on repeated individual interactions between legislators, which, over time, generate a system of legislative voting patterns sufficiently stable for legislators to lessen the problems inherent to policy making and successfully pursue their goals. The dissertation provides empirical evidence that the Colombian Congress has developed a structure of individual relationships that systematically influences legislative voting. The dissertation concludes with key implications for the understanding of legislatures.