[eng] Through a rich panel of Spanish manufacturing companies, this study examines the hypothesis that the formation of inter-organizational complementarities in R&D depends on the type of alliance chosen by a firm to leverage its own RΔ To test this hypothesis, the study compares the capacity of different organizational designs of internal and external R&D activities to produce complementarities. The results indicate the existence of complementarities for cases where firms combine their own R&D with research collaboration. No complementarities are found for cases where firms adopt both intramural and R&D outsourcing jointly. Additionally, a comparison of the factors driving choices on R&D reveals that the use of 'innovation management practices' and the presence of 'technological opportunities' relate more to the adoption of research collaboration than to the adoption of R&D outsourcing. These findings are relevant as they may explain the reported differences in the production of complementarities.