Indonesia’s party system has been undergoing increasing institutionalization and stability. These can be seen in a number of indicators such as patterns of parties’ votes, medium-term stability of votes, electoral volatility, and changes in parties’ ideological positions. This institutionalization and stability emerged despite the declining trend of Indonesia’s democratic quality. Drawing on the results from five democratic elections between 1999 to 2019, this chapter finds that these outcomes have been possible given the specific structuring mechanism played by the electoral rules. While the electoral rules have been consistently raising the standard barriers to entry for new players, the timing of issuance and the expected outcomes of those rules reinforce the current system. This chapter argues that it is the stability and institutionalization of the party system that helps maintain Indonesia’s status as an electoral democracy, thus saving the country from getting into the deeper abyss of democratic regression.