This article examines the relationship between co-opetition, the simultaneous cooperation and competition, and the success of e-business in small and medium-sized enterprises (SMEs). In this context co-opetition is understood and operationalized as a combination of sourcing and alignment capabilities of the SMEs and the cooperative orientation of the business partner. The exploratory findings from interviews followed by a survey of 339 SMEs in three European countries show that cooperation in e-business alliances is positively correlated with e-business value-creation in terms of efficiency, complementarities, lock-in and novelty. The research has implications for business managers in both small and big companies as they make decisions regarding inter-organizational cooperation.