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Over the past two decades, two seemingly separate disciplines, social entrepreneurship and sustainable microfinance, have both matured and converged so that the latter has become a major example of the successful application of the former. Sustainable microfinance shows that banks and commercially-oriented NGOs can "do well by doing good" since they can generate considerable profits while at the same time having a strongly positive impact on development. Sustainable microfinance institutions are innovative creators of social value in that they pursue business opportunities where financial performance and social impact complement rather than compete with each other. They apply conventional banking precepts in an unconventional manner, creating commercially viable financial institutions that double as agents of social change. Despite the many opportunities presented by scaling down or scaling up, there is still a vital role for non-commercialized microfinance. It is essential to match the appropriate institutional model, whether a bank, finance company, membership-based organization, or subsidized NGO, with the mission of the microfinance organization. The guiding principles should be institutional diversification, product differentiation, and market segmentation.