Global competition has increased the pressure for firms to develop new and efficient processes in ways that are perceived to be legitimate. At the same time, there has been a realization that engaging with open innovation can improve competitiveness. Our study aims to address two research questions: (a) How does engaging with open innovation support an organization's process innovation? and (b) How does the motivation to achieve legitimacy affect the relationship between engaging with open innovation and process innovation? We use arguments from the resource‐based view to explain how open innovation influences an organization's likelihood of introducing new processes. We then use arguments from institutional theory to explain how the motivation to achieve legitimacy moderates this relationship. We test our conceptual model using data from the European Community Innovation Survey administered by the U.K. government. Our findings and theoretical development support the notion that engagement with open innovation will increase the likelihood of introducing new processes and that the motivation to achieve legitimacy will affect this relationship. However, this moderating effect will be different depending on how engagement takes place. It will be positive on co‐operation with external parties, and negative on the use of information. Therefore, when organizations co‐operate with external parties and are motivated to achieve legitimacy, the likelihood of introducing a new process will increase. However, the effect is opposite in the case of use of external information. These findings contribute to the understanding of the relationship between open and process innovation.