Paul M. Walker points out the importance of three seventeenth-century manuscripts which, according to him, reflect the origins of the late Baroque monothematic fugue. The documents present a new "model" with specific criteria to write monothematic fugues. Walker suggests that the criteria presented in these manuscripts are first found in seventeenth-century Italian violin ensemble fugues. This thesis traces the development of seventeenth-century monothematic fugues and how they compare with the criteria presented in the manuscripts, with a particular emphasis on Italian violin ensemble fugues. The manuscripts indeed present a new "model" to write monothematic fugues as compared to earlier models. Generally speaking, the criteria included in the manuscripts are more present in monothematic fugues found in seventeenth-century violin ensemble music than in keyboard music of the same period. However, many of these imitative pieces present characteristics of fugato (rather than "true" fugues) and cannot be compared with the manuscripts' criteria. Therefore, the documents are important from a theoretical standpoint but their practical application in seventeenth-century violin music is not as clear or systematic as Walker implies.