JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Academy of Management is collaborating with JSTOR to digitize, preserve and extend access to The Academy of Management Journal.We integrate resource dependency and institutional theory to argue that resource scarcity drives, and legitimacy enables, institutional change. Building on a historical account, we examine the sources and timing of innovation departing from standard human resource practices using event history analysis of over 200 principal offices of large law firms. Offices with human resource scarcity innovated to acquire alternative resources; highly prestigious offices had the legitimacy to be first or early adopters. Our findings highlight the value of looking to the resource side and to the notion of legitimacy in building an institutional theory of change.