Large corporations have aimed to establish partnerships with startups to turn them into drivers of corporate innovation. Lately, collaboration initiatives with startups have multiplied, but this interaction has received little attention from organizational studies. This article aims to fill in this gap by identifying the determining elements of the interaction between cooperatives and startups in the context of open innovation. A Qualitative Comparative Analysis (QCA) was conducted with representatives of credit cooperatives and Brazilian startups. The results led to five constructs of interaction for innovation between credit cooperatives and startups – objective, decision-making, relationship, knowledge flows, and experience. The conditions required for open innovation in this context, resulting from the QCA analysis, were pointed out, and a leading framework of collaboration between credit cooperatives and startups was proposed based on the constructs identified. These results might assist cooperatives and startups involved in open innovation initiatives.