Introduces the main argument, that much about the instrumental music of the later eighteenth century can be grasped with reference to the concept of sociability. The concept is defined and placed alongside other rubrics such as expression, language and behaviour. Sociability is separated into affective and technical spheres. Haydn, a market leader both critically and commercially, is the central figure for the study. The modern reception of later eighteenth-century style is discussed with particular reference to Haydn and Mozart, noting the critical tendency to occupy a moral high ground above the image of a ‘shallow sociability’, and concluding with the challenge ‘When else … in Western music history has a whole style been so often understood negatively, as a problem in need of a solution?’. Then I investigate the listener-friendliness of the style: the pronounced orientation of this music towards a listening subject was historically novel. This music both challenges listeners and puts them at their ease.