More than a third of the world's population (2.4 billion people) lacks access to adequate excreta disposal. Four in five of these unserved people are in Asia, with approximately one in five in both India and China, respectively. Even in large Asian cities, less than half of those served are using sewerage systems; the others use on-site systems, from pit latrines to septic tanks. Most have been installed by householders or builders employed by them, rather than by government or municipal agencies. Governments, international agencies and municipalities can never hope to meet the immense gap in provision unless they promote sanitation with a marketing approach. A latrine is a consumer durable which must be sold. It is often considered that the constraint to increasing sanitation coverage is a lack of demand, but there is often a lack of supply of appropriate products, and latrine designs are often too expensive for the poor, requiring subsidies which are captured by the better-off. More market research is needed to define the right product and how best to stimulate demand. Where subsidies are used, the promotion, not the production of the latrines must be subsidised to prevent middle-class capture of the subsidy. Promotion is probably best performed by different agencies from those that build latrines. The expertise and marketing capacity of the private sector needs to be brought into play, and public bodies must learn to assist it effectively in bringing sanitation to all.