After the papers of D. Burry and J. A. Green, the author gives another approach to the theory of Scott modules, p-permutation modules \((=\) trivial source modules) and lower defect groups, using systematically the Brauer morphism. In the first part new proofs are given of results of Scott, Alperin and Burry, and in the second part some nice and natural results on p-permutation modules are proved. Further (partly related) results will appear in a forthcoming paper by the author and G. Robinson.