During its history, the violin has been associated with an abundance of other instruments, not to mention its particularly close relationship with the human voice, to which it has often been compared. To chronicle this would be a formidable task, but fortunately, over a number of centuries, musical taste has favoured a quite limited range of specific groupings which quickly acquired the status of ‘genre’. A Haydn string quartet suggests not just an instrumental combination but a specific mode of treatment, and it is such characteristic forms rather than any ad hoc instrumentation which must demand the closest attention. For the present purposes an ensemble is defined rather arbitrarily as any group of two or more instrumentalists, but excluding compositions for violin and keyboard, the main concern being that repertory categorised today by the equally arbitrary term ‘chamber music’. The New Grove Dictionary defines this as ‘music for small ensembles of solo instruments, written for performance under domestic circumstances’, but this is especially inadequate for the seventeenth century, when small ensemble music need not have been performed in ‘chambers’, while ‘chamber ensembles’ may have been used as ‘orchestras’ in public theatres or churches. Some flexibility has therefore seemed advisable, at least for the first two centuries of this development.