Advocates of promoting handwashing with soap agree that this behavior has important health benefits across the globe. Efforts, both large-scale and focused, are underway worldwide to promote handwashing with soap at the community level (www.globalhandwashing.org). Although there is broad agreement about the health benefits of promoting handwashing with soap, there is not similar agreement about the best ways to measure the behavior that these promotion programs set out to change. The reality is this: there is no universally applicable method for measuring handwashing behavior that is valid, relevant, affordable, and logistically feasible for the various settings in which such behavior might need to be measured. The aim of this document is to describe techniques and to propose strategies for measuring handwashing behavior for a variety of scenarios.