Building on the NRBV, eco-innovation, and supplier involvement literature, our results suggest that supplier eco-innovationcapabilities and alliance partner diversity can influence the development of inter-organizational eco-innovations. We contribute tothe eco-innovation literature by undertaking one of the firstempirical studies of the determinants of inter-organizational ecoinnovation when suppliers are involved in NPD. Using the researchcontext of the Toyota supplier association, our empirical analysisreveals that supplier electric capabilities and hybrid capabilities areassociated with a significant increase in the degree of ecoinnovation co-patenting. However, we find mixed results for theextent to which alliance partner diversity moderates the relationship between supplier eco-innovation capabilities and copatenting. Finally, we have also identified some of the similaritiesand differences between Japanese automakers in how they developinter-organizational eco-innovations within their suppliernetworks.