Open innovation (OI) is an important phenomenon in a global marketplace where knowledge is distributed and individual firms no longer have a monopoly on the best talent. As firms increasingly search for innovative external ideas and solutions, an obvious problem is how to source high-quality contributions externally. A more specific problem is how firms motivate in-bound, non-pecuniary contributions for important activities like customer co-creation, where market-based transactions are not appropriate. A proliferation of papers on OI highlights the need for an integrative review about what motivates individuals to contribute ideas for free, and how firms can use this knowledge to achieve their OI goals. This paper presents a review of the disparate studies on the motivation of individuals to participate in open innovation without immediate monetary gain. We identify 11 distinct individual motivational factors, and find that many initially intrinsic motivations are linked to payoffs for contributors that only accrue with time - something we term ‘delayed-pecuniary motivation’. We use our findings to build a framework that illustrates the importance of this temporal view of OI motivations and we suggest interventions to engage contributors for different kinds of innovation problems.