Open innovation has become a mainstream phenomenon in the current business landscape. However, despite the fact that innovation projects generally have different attributes (e.g., complexity and uncertainty), most studies on open innovation have only considered firm-level characteristics (e.g., firm size and firm openness) to determine how to manage open innovation successfully. Project-level studies on open innovation management are still scant-There are only a few conceptual and qualitative articles on the topic, and there is a lack of quantitative insights. Based on a survey designed to collect detailed data from 201 innovation projects undertaken by American firms, this article provides a quantitative cross-project analysis of how two, key innovation project attributes (i.e., complexity and uncertainty) are related to five factors for successful open innovation management: 1) openness level, 2) external partner choice, 3) open innovation mechanism choice, 4) collaboration process formalization, and 5) internal firm practices. This exploratory study contributes to the open innovation literature by highlighting the importance of microfoundations (i.e., innovation project attributes) in successful open innovation management. This article concludes by suggesting a number of relevant project-level future research opportunities in the field of open innovation management, and some methodological recommendations on how to address such opportunities.