Unlike other assets, data’s value increases when it is shared and reused. Whereas organizations have traditionally exchanged data vertically with other actors along the value chain, we observe that they increasingly share complementary data assets with others, even at times with their competitors, to address business and societal challenges. Research on these new forms of horizontal data sharing and the emerging data ecosystems is still scarce. Building on the theory of communities of practice, we study a pioneer data sharing community comprising more than 20 multinational companies that developed an innovative approach to pool data management efforts. We derive eight design principles for horizontal data sharing, which we cluster according to the following dimensions: domain of interest, shared practice, and community. By offering prescriptive design knowledge, our findings make an important contribution to the emerging literature on cross-company data sharing. Our research also provides practitioners with actionable insights on how to establish and operate data sharing communities effectively.