Party politics in Indonesia’s current democratic regime takes place within the parameters of a heavily fragmented multi-party system. Factionalism exists in most parties, but the influence of factions on internal party dynamics is only weak to moderate. Where factions exist, they are usually driven by clientelism and patronage rather than the representation of social cleavages, ideological differences, or regional affiliations, although traces of programmatically infused factionalism do persist in some parties. The intensity of factional conflicts in Indonesia’s young democracy has varied significantly over time and across different parties. While temporal variations are mostly related to changing institutional incentive structures, disparities between individual parties can be attributed to different organisational histories and structures as well as divergent levels of rootedness in social cleavage structures. It is noteworthy that several Indonesian parties have relatively deep roots in society and, in some cases, close links to long-established civil society organisations that preceded party formation. Given these constraints on more severe factionalism, damaging effects on governance have been fairly limited. The most debilitating effects of factionalism have been felt within the parties themselves, whereas government effectiveness and coalition formation has, ironically, sometimes benefitted from factional disputes.