Access to relevant external knowledge is crucial for a firms' competitiveness in innovation-driven industries. This thesis focuses on how different forms of proximity affect a firm's ability to access such knowledge. We consider the influence of being co-located in space, of being embedded in a network, and of being active in similar knowledge domains. By integrating these three proximity perspectives, we contribute to various disciplines such as economic geography, organizational sociology and innovation studies. Further, we investigate the make, buy or ally strategies that pharmaceutical firms employ to maximize the probability of innovation (finding new drugs). Our findings suggest that firms employ multiple governance structures simultaneously, even when targeting similar innovations. These insights contribute to our understanding of the boundaries of the firm.