Differentiated prices, bundling, Web auctions : firms' pricing practices are evolving. When there is no market or for customised pricing, the willingness-to-pay concept seems to be interesting. This article aims at presenting a synthesis of the marketing research stream relative to willingness to pay. First, a definition of the concept is given and compared to other similar concepts, notably reference price and acceptable price. Then the methods of measurement are presented, compared to those used to measure elasticity and criticized. Furthermore, the research on external determinants of willingness to pay is commented. Finally, numerous directions for further research are proposed.