The overall goal of our research is to understand why nature has triplicated the spectrum of particles. These three "flavours" exhibit a quite peculiar pattern of masses and mixing parameters, including the violation of the CP symmetry, which is otheriwse inherent in the construction of the Standard Model of particle physics. With the current as well as with future experiments all three generations of particles can be investigated in detail. In particular, also the "heavy" top and bottom quarks can be produced in large numbers and hence precision measurements can be made. These precise measurements need to be accomanpied by theoretical developments, which are pushed forward in our group. One one hand, precise calculations of the observed processes are needed, on the other hand, also appropriate parametrizations as well as models for physics beyond the Standard Model are needed to make full use to the large amount of data to be expected in the near future. Specifically, the following topics are dealt with: Precision calculations within the Standard Model in order to obtain precise predictions as well as precise extractions of the parameters. This is done using effective field theories, such as heavy mass expansion for heavy quarks, QCD sum rule estimates for the hadronic matrix elements and, if no QCD based methods are available, also model for form factors. Development and investigation of QCD based methods for precision calculations. This includes estimates of hadronic matrix elements and form factors entering the calculations of rates and cross sections. Usage of approximate symmetries of QCD to predict relations between processes and to determine various hadronic parameters. Effective field theory parametrizations of possible effects from physics beyond the Standard Model, based eg. on the approximate flavour symmetries of the Standard Model or by embedding this approximate flavour symmetry into a larger symmetry group.