This investigation deals with three leading representatives of the North German Pre-Clasaical School. The sonatas of W.F. Bach and G. Benda have as yet received little attention. E .Bach, on the other hand, was always regarded as the most influential composer in the early history of the German piano sonata. Nevertheless, the existing literature on C.P.E. Bach is concerned with certain aspects or his works only or is devoted to introductory discussions. The aims of this research is to trace the development of the piano sonata and in particular the evolution of the 'sonata form' within the German Pre-Classical School. The works of W.F. Bach present the earliest stage in this development, which reaches its culmination with C.P.E. Bach. The final consolidation of the sonata form is then achieved in the piano sonatas of G. Benda.