Creating and exchanging tacit knowledge is widely considered as a key driver for interorganizational collaboration, especially in the context of open innovation. Yet, it is less well understood how organizations jointly transform tacit knowledge into explicit solutions, which often is a critical step in collaborative innovation processes. This paper explores this process in an embedded longitudinal case study of a loosely-coupled multi-partner open innovation program. We find five distinct mechanisms that drive codification from tacit knowledge to explicit knowledge and solutions. Furthermore, these mechanisms vary with the nature of tacit knowledge: whereas data sharing and direct expert interaction are key drivers for exchanging weaker tacit knowledge and making it explicit, creating and codifying strong tacit knowledge occur through radical goalsetting and proof-of-concept development. Different contextual and partner-specific factors appear to enable the effectiveness of each mechanism. These findings contribute to the literatures on tacit knowledge transfer, interorganizational collaboration, and open innovation.