The development of information processing systems requires models, calculi, and theories for the analysis of computations. It is well understood by now that more complex software systems cannot and should not be constructed in one step. A careful, systematic, and disciplined structuring of the development process is most adequate. It should start from basic requirement specifications in which aU the relevant details of the problem to be solved are formalized. The envisaged solution should be developed step by step by adding more and more details and giving evidence-in the best case by formal proof-to show the correctness of the developed steps. The development ends if a description of a solution is obtained that has aU the required properties. The Summer School in Marktoberdorf 1992 showed significant approaches in this area to refinement calculi, to models of computation, and as a special issue to the treatment of reactive timed systems. Like in the many summer schools before, the success of the 1992 Summer School was not only due to the excellent lectures, but even more due to the brilliant students taking part in the discussions at the summer school, the exchange of different views, and the recognition of the similarity of a number of different view points. These were some of the most important contributions of the summer school. fu the following the proceedings of the summer school are collected. They show the maturity of the field in an impressive way.