We have seen that the NSE technique can be applied for a variety of inelastic scattering processes and for both magnetic or non-magnetic samples. But the real conclusion of this introductory paper is in fact contained in the contributions which follow. At this point I should just like to express my gratitude for many stimulating discussions to a large number of colleagues, first of all to the authors of this volume and to many others at the ILL together with those I have already thanked in the preface. I should particularly like to thank the audiences who attended the talks I have given at various places, whose questions and sometimes difficulties with these ideas were certainly invaluable for my own understanding.