This dissertation studies the origin of new organisational forms. It focuses on organisations that challenge existing institutional boundaries, specifically the boundaries between for profit and not for profit providers of financial services. It builds on research on the origins of the microfinance industry in Bolivia; and particularly on the creation and development of BancoSol and Los Andes, the two pioneering organisations. This research involved in-depth interviews and analysis of industry-specific documents and newspaper files.The study builds on three research streams: collective strategy, institutional theory, and evolutionary entrepreneurship. It proposes an overarching process-model that bridges these three bodies of work and advances our understanding of three key dynamics in the creation of new organisational forms: (1) the combination of hitherto unconnected principles and practices; (2) the leverage of support and acceptance for new organisational forms; and (3) the development of endurance for the new form.The study argues that these three dynamics occur within a nonlinear process that includes three overlying stages. The first stage involves the creation of an entrepreneurial team to launch the organisations. This team includes individuals from fields with divergent principles and practices (e.g. for profit and not for profit). The second stage involves negotiations with institutional actors to leverage support and acceptance for the novel organisational form. The third stage involves decisions, actions, and interactions that promote internal coalescence and defend the organisations from external challenges. I have labeled this process-model social entrepreneurship. The process is predominantly social as the three dynamics are defined by the social assets and relations of actors. It is predominantly entrepreneurial as it destroys existing boundaries across fields and generates an enduring combination of principles and practices previously unconnected.