Hand washing with soap and water is a simple way to reduce the spread of disease. It doesn’t require complicated technology, it’s usually affordable, and even young children can do it. Yet many people don’t wash their hands when they should: before touching food, after using the toilet or after cleaning a baby’s bottom. Because bacteria, parasites, and viruses can easily spread when people don’t wash their hands, finding ways to boost hand-washing can significantly reduce the risk of potentially fatal diarrheal and respiratory infections for children. The World Bank is committed to ending poverty and giving everyone an equal chance in life, and promoting healthy habits can help make this happen. To further these goals, the World Bank supported a project to encourage people to use soap and water to wash their hands at critical times throughout the day. Impact evaluations from Peru and Vietnam, two of the countries where the project was implemented, showed that it isn’t easy to change behavior, at least not on a large scale. In Vietnam, using mass media campaigns and face-to-face communication did raise awareness, but it didn’t lead to any observable changes in how often or when people washed their hands. In Peru, there was a measurable boost when a mass media campaign was twinned with school handwashing activities for children. As the studies show, washing hands is simple, but getting people to do it at the right times isn’t that easy, and the right mix of programs to change behavior on a large scale still needs to be devised.