Embracing business-to-business open innovation (B2B OI) can enable firms to remain competitive in an increasingly saturated business environment. Whilst B2B OI is generally undertaken to serve the needs of a specific innovation project, previous research has mainly studied it from the firm-level perspective. Accordingly, the number of project-level studies on B2B OI, especially empirical, remains limited, resulting in an incomplete understanding of B2B OI management. In this editorial, we briefly review the B2B OI literature, discuss the importance of studying B2B OI at project level, and describe how each of the six articles included in our special issue contributes to this field. Moreover, we suggest future research opportunities with regard to issues and topics that remain largely under-investigated in project-level B2B OI, but which also open up to a multilevel perspective.