This dissertation explores how entrepreneurs form strategy, organize, and compete in nascent markets that emerge within institutional fields. In these settings, entrepreneurs face the dual challenges of creating successful ventures while also navigating (and perhaps changing) the institutional field. Despite the challenges, nascent markets within institutional fields offer enormous potential for both financial success and social impact--a particularly attractive combination for mission-driven entrepreneurs. Yet, prior research overlooks how entrepreneurs form successful strategies, organize their ventures, and compete with rivals in these challenging but important settings. Given limited theoretical understanding and empirical evidence, I use a multiple-case theory-building approach to explore the nascent MOOC (massive open online course) market that emerged within the field of U.S. higher education. I present three related emergent theoretical frameworks. The first, "Mavericks and Diplomats," identifies two contrasting but effective processes to form strategy in nascent markets within institutional fields. The second, "Mission and Money," explores competition over time between ventures that organize as hybrids by integrating the logics of multiple institutions. The third, "The Pain of the Pivot," unpacks the often-painful processes of enacting significant changes in a venture's strategy, commonly referred to as pivoting. Jointly, these three theoretical frameworks provide novel insights into how mission-driven entrepreneurs form strategy, organize, and compete when new markets collide with powerful institutions. Overall, this dissertation contributes to strategy, entrepreneurship, and organizations research and practice. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]