This paper critically reviews the existing research on the cost-effective prevention and treatment of diarrheal diseases, and identifies research priorities in this area aimed at finding ways to reduce the diarrheal disease burden. In contrast to the empirical knowledge base that exists for traditional child health programs to reduce diarrheal morbidity and mortality, evidence on the relative effectiveness and costeffectiveness of various environmental health interventions is limited and subject to significant methodological concerns. There is a limited understanding of the determinants of long-term water and sanitation technology adoption and behavior change at the individual level. Even less is known about how collective action problems in water and sanitation infrastructure maintenance can be overcome. An agenda for future research includes evaluating alternative transmission interruption mechanisms, improving understanding of the determinants of individual-level technology adoption in the water and sanitation sector, and assessing the quality of infrastructure maintenance under different management schemes.