This paper is meant to be a guide for banks, microfinance institutions (MFIs), and donors who are considering applying credit scoring as part of their business model. The research team draws on the experience of microlenders from three continents to illustrate a four-step framework for designing and implementing custom credit scorecards. The framework is flexible, does not advocate any one rigid methodology or technology, and is thus appropriate to any organization with a clear strategy and some experience lending to its target market.