The association between hygiene, sanitation and health is well documented, yet thousands of children die each year from exposure to contaminated fecal matter. At the same time, evidence on the effectiveness of at-scale behavior change interventions to improve sanitation and hygiene practices is limited. In response to the preventable threats posed by poor sanitation and hygiene, the World Bank's Water and Sanitation Program (WSP) has launched two large projects, Global Scaling Up Handwashing and Global Scaling Up Rural Sanitation, to improve the health and welfare outcomes for millions of people in developing nations. These projects have been implemented by local and national governments with technical support from WSP. Researchers from the World Bank and Inter-American Development Bank studied these two projects impemented in rural Tanzania, with the objective of tracing the causal chain from hygiene and sanitation promotion to changes in child health outcomes. The research team specifically tested for potential interaction effects of combining handwashing and sanitation interventions. The study was designed as an effectiveness trial to provide evidence for policymakers and government implementing agencies planning at-scale campaigns. From mid-2009 to early 2011, two interventions were rolled out in ten districts of Tanzania following a factorial experimental design. 181 rural wards included in the study were divided into four groups to receive the handwashing intervention alone, the sanitation intervention alone, both the handwashing and sanitation, or neither intervention (control group). A baseline was planned for early 2009 but was aborted due to logistical field challenges. Since random assignment of implementation was adhered to, the study continued and researchers conducted an endline survey in 2012, approximately one year after the conclusion of the program. The survey included 3,619 households and 5,768 children under five years old.