The goal of global scaling uphandwashing is to reduce the risk of diarrhea and thereforeincrease household productivity by stimulating andsustaining the behavior of handwashing with soap at criticaltimes in the lives of 5.4 million people in Peru, Senegal,Tanzania, and Vietnam, where the project has beenimplemented to date. The structure of this report proceedsas follows: In chapter one author provide an overview of theglobal scaling up handwashing and global scaling up ruralsanitation projects, as well as background on thehandwashing project in Vietnam. Chapter two details themethodology that underlies the impact evaluation, andprovides details on the sampling design, sample selection,and field work protocols. The baseline findings for generalhousehold characteristics, handwashing behavior, childhealth, and child growth are presented in depth in chapterthree. In chapter four authors conclude with a summary ofthe next steps of the impact evaluation study.