In November 2010, PLoS Medicine published a four-part series on water and sanitation. In the first article, Jamie Bartram and Sandy Cairncross argue that the massive burden of ill health associated with poor hygiene, sanitation, and water supply demands more attention from health professionals and policymakers. In the second article, Paul Hunter and colleagues focus on water supply and argue that much more effort is needed to improve access to safe and sustainable water supplies. David Trouba and colleagues discuss the importance of improved sanitation to health and the role that the health sector can play in its advocacy in the third article. And in the final article, Sandy Cairncross and colleagues outline what needs to be done to make significant progress in providing more and better hygiene, sanitation, and water for all. The active involvement of health professionals in hygiene, sanitation, and water supply is crucial to accelerating and consolidating progress for health, argue the authors.