This thesis explores the determinants of political representation. Political parties and other agents, such as factions and individual politicians, represent citizens by providing either policies or particularistic services. At a descriptive level of analysis, these types of goods entail the two extremes of a continuum on which it is possible to locate party systems, parties and individual legislators across countries. Recent literature explaining patterns of political representation in Latin America do not provide compelling evidence regarding the incentives political actors have to provide policy or service to constituents. Most of the literature on parties holds that competition can be either electoral or ideological, underscoring that these two dimensions are analytically different and that this difference has important implications for the type of representation that parties provide: different combinations of these two dimensions (electoral and ideological) lead to different types of political representation, measured as the type of goods provided by parties in terms of policy or service to constituents. This dissertation contends that these two types of goods can be better explained by the type of political competition in which parties are involved. To provide a new explanation for the variation observed across countries, I elaborate a new typology of political competition and use it to compare fifteen Latin American cases circa 2003. This comparative analysis allows me to map the type of party competition for each country in the region, as well as the predominant type of representation provided by parties in the form of policy or service. This analysis is followed by an in depth case study of the Uruguayan party system, which is the extreme case in policy provision at the comparative level. The thesis asks how Uruguayan parties changed over time from a strongly service oriented model towards the current policy oriented model. My explanation revolves around the evolution of party competition, from low levels of electoral competitiveness without clear policy stances towards increasing levels of electoral competitiveness and moderately high levels of ideological polarization after 1971. The confluence of these two factors has driven parties to compete on policy rather than service in the last decades.