The purpose of this study is to empirically investigate the firm- and regional-level determinants of a firm’s adoption of open innovation practices. In particular, we categorise sixteen Korean regions into seven regional innovation types to account for each regions’ varying innovation conditions. Using data from the Korean Innovation Survey and a hierarchical linear model, we find that firm-level factors such as firm size, R&D innovation capability and the number of networks for absorbing external knowledge and regional-level factors such as local government R&D funds matching had a significantly positive effect on open innovation. We also find that of the firm-level determinants, the number of networks had a strong effect on open innovation, and that this differed by regional innovation type. Based on these findings, we argue that innovation policy should strive to stimulate open innovation through measures that take each region’s innovation resources and environment into account, rather than attempting to look for a single optimised model for all regions.