This thesis is concerned with the guitar music of Nathanael Diesel. The music is contained in two manuscript collections, Ny Kgl. Saml. 110, and Gl. Kgl. Saml. 377. This study has centered on the duets for guitar of which there are ninety-six movements. Sixty-five of these are to be found in twelve suites. The remaining music in the collections is for guitar solo. This is the largest collection of music known for two guitars and various combinations of instruments with guitar. Its uniqueness is only surpassed by its quality. This study has shown that Nathanael Diesel must be considered an important link between the Baroque and the Classical period because of his advanced compositional technique for the guitar. In many of the works he shows a very definite tendency toward writing with an Italianate melodic style, one which does not appear in the works of his...