Collaboration and competition have long been considered separate modes of interaction between firms. In this study, we turn our attention to co-opetitive interfirm linkages, that is, relationships in which firms compete and cooperate with one another at the same time. Drawing on a sample of 287 start-ups in the emerging US clean transportation industry (2008-2012), we quantitatively examine and compare co-opetitive and non-co-opetitive ties that entrepreneurial firms get involved in. Our findings show that co-opetitive and non-co-opetitive inter-organizational relationships have differential effects on start-ups’ ability to innovate and to attract financial investment. Our findings hold important implications for research interested in the interplay between competition and cooperation, innovation, and entrepreneurship.