Why is it that so many people in our world still lack access to a toilet? Many developing countries have met their Millennium Development Goal target for access to clean water but still lag far behind their goal for access to improved forms of sanitation, especially in the rural and unplanned peri-urban settlements that are inhabited by the poorest of the poor. A great deal of thinking, funding, and time has been invested recently in developing clever new toilets, but there is also a need to better understand and get the most out of the sanitation facilities to which many poor people already have access, such as basic pit latrines. There is an urgent need for longer lasting, sustainable sanitation solutions, but this should look beyond just new toilet designs and include providing sanitation services, enabling community leadership in sanitation programmes, and training the in-country sanitation specialists of the future. Achieving sustainable sanitation for all is not just an engineering challenge, nor is it only for economists and social scientists; multi-disciplinary efforts are critical to achieving successful outcomes. As sanitation needs expand and justification is sought for large-scale infrastructure projects, especially in booming urban areas, greater recognition is needed that investment in sanitation infrastructure is not only about improving health, but will also ultimately lead to significant economic returns.