This study has two divisions: Part I, an historical and analytical summary of the emergence and development of the divertimento and the serenade in the eighteenth century, and Part II, the culmination of these structures in the works of W. A. Mozart. Two primary purposes are envisioned: 1) to further our knowledge of how German Gesellshafts-musik evolved toward its peak in the second half of the eighteenth century, and 2) to furnish a useful analytical handbook of Mozart's works in these genres.