<p>Although the impact of governance on interfirm relationships has been extensively studied, the role of information technology (IT) as a governance mechanism in platform ecosystems remains underexplored. Drawing on agency theory, this research examines the differing impacts of IT monitoring and reputation badges on participation slackness and value co-creation of digital platform complementors, as well as the moderating role of IT support. The empirical findings from the survey of 278 complementors and secondary datasets indicate that IT monitoring and reputation badges mitigate complementors’ slackness, while reputation badges encourage complementors’ value co-creation behaviors. Furthermore, the negative relationship between reputation badges and participation slackness and the positive effect of reputation badges on value co-creation are stronger when IT support of the platform is high. Similarly, the positive impact of IT monitoring on complementors’ value co-creation is reinforced when IT support is high. Overall, the study confirms the impact of IT governance on various types of complementor behaviors and highlights the contingent role of IT support.</p>