This paper is motivated by a desire to clarify the definition of ‘openness’ as currently used in the literature on open innovation, and to re-conceptualize the idea for future research on the topic. We combine bibliographic analysis of all papers on the topic published in Thomson's ISI Web of Knowledge (ISI) with a systematic content analysis of the field to develop a deeper understanding of earlier work. Our review indicates two inbound processes: sourcing and acquiring, and two outbound processes, revealing and selling. We analyze the advantages and disadvantages of these different forms of openness. The paper concludes with implications for theory and practice, charting several promising areas for future research.