This paper describes important trade-offs that microfinance practitioners, donors, and regulators navigate. Drawing evidence from large, global surveys of microfinance institutions, the authors find a basic tension between meeting social goals and maximizing financial performance. For example, non-profit microfinance institutions make far smaller loans on average and serve more women as a fraction of customers than do commercialized microfinance banks, but their costs per dollar lent are also much higher. Potential trade-offs therefore arise when selecting contracting mechanisms, level of commercialization, rigor of regulation, and the extent of competition. Meaningful interventions in microfinance will require making deliberate choices - and thus embracing and weighing tradeoffs carefully.