This dissertation contributes to a research agenda on the role of party systems and political parties on political corruption. Previous research found multiple and contradictory evidence regarding the role of electoral systems on corruption. These controversies have to do with two main problems: the overlooked effect of political parties’ organization on political corruption and problems with corruption measures. I propose two different mechanisms that affect the relationship between politicians and citizens and different measures that impact the previous results. The dissertation is divided into three papers. In the first one, I analyze the role of political parties’ nationalization in promoting programmatic linkages between political parties and citizens (the first mechanism), and decreasing both the perception of corruption and actual political corruption. The second paper analyzes party system nationalization and its effects on accountability (the second mechanism) and corruption. Both papers are quantitative and use mediation analysis to test the arguments empirically. In the third paper, I develop an index to measure the risk of corruption in both party systems and political parties. Using legislation about party laws, electoral management bodies, party funding, lobby, and political parties’ statutes, I calculate the risk for 18 Latin American countries and 85 political parties in these countries. Together, these three papers contribute to the knowledge of political parties’ organization (territorial and internal) and its effects on the perception of corruption, political corruption, and risk of corruption.