Abstract: The superior repayment performance of the clients of microfinance institutions - when contrasted with banks - and the robustness of this repayment behavior during periods of severe systemic shocks have attracted much speculation. This dissertation formally addresses these issues, by exploring the relationships between overindebtedness and alternative lending technologies and contract designs. Data for 1997-2001, from a household survey taken during the overindebtedness episode of the Bolivian financial sector, are used to test the hypotheses. Overindebtedness is an outcome of a loan contract that does not correspond to the original expectations of the borrower, the lender, or both. Repayment difficulties may result from unwillingness to repay, inability to repay, or actual repayment only after extraordinary capacity is generated through costly actions. Costly actions reflect efforts or outcomes beyond what the borrower had planned at the time of contract. Any credit relationship characterized by willingness and ability to repay without exceptional cost implies the absence of overindebtedness. Overindebtedness may result from the opportunistic behavior of lenders, the opportunistic behavior of borrowers, unexpected adverse systemic shocks, or limitations of the lending technologies in forecasting ordinary repayment capacity. The dissertation builds a conceptual framework for the analysis of overindebtedness among microfinance borrowers. The model considers the intertemporal choices of different types of borrowers - when faced with unexpected adverse shocks and the need to reassess their repayment options - guided by the value of relationships characterized by different contract terms and the opportunity costs of the extra efforts required. The dissertation establishes a previously unidentified link between a high degree of extraordinary repayment capacity (both extraordinary willingness and extraordinary ability to repay) and the high repayment rates observed among MFIs. These rates are explained both by the ability to elicit strong incentives to repay and the opportunities these households have to generate extraordinary ability to repay. Thus, given similar ability across lenders to induce ordinary repayment capacity, the strength of microfinance lending technologies comes from their ability to create incentives for the borrower to engage in extraordinary costly actions and their capacity to identify households with a high probability of success at generating extraordinary ability to repay.