Rousseau's one-act opera 'Le Devin du village' (1752-53) long remained a popular work in Paris and in other countries. It maintained this position over decades of radical change in musical language because Rousseau created a unique but sophisticated style in an approachable kind of idiom. And as author of the words as well as the score, Rousseau lays claim to be compared with Richard Wagner a century later, both for this achievement and in opening various pathways for others. This article first focuses on the main ingredients of Rousseau's new type of melody: popular French song or 'vaudeville'; one-act 'song-operas' recently composed for the Marquise de Pompadour's court theatre; and the 'Pergolesi' style from Italy. The underlying but easily audible thematic unity displayed in 'Le devin du village' is then traced. Finally the influence of the Rousseau style on others is outlined, first melodically and structurally in Dauvergne's 'Les Troqueurs' (1753) and then in early opéras-comiques by Egidio Duni and Pierre-Alexandre Monsigny, these conclusions being based on criteria established in the first part of the investigation.