In this paper, we empirically analyze how strategic alliances affect the innovation output of the firms forming the alliance. We find a positive effect of R&D-related strategic alliances on corporate innovation, as measured by the quantity and quality of patents filed. This effect is stronger for firms led by CEOs with higher general managerial skills, firms with greater experience from earlier alliances, and firms operating in R&D-intensive industries. Furthermore, the innovation-fostering effect of strategic alliances is more pronounced if alliance partnering firms share a common institutional blockholder or have a higher degree of technological proximity. We also document, for the first time in the literature, a unique contractual mechanism through which firms share the benefits of innovation with their alliance partners, namely, “co-patenting.”