Abstract: We consider the dynamics of a large number N of interacting, nonrelativistic bosons in the mean field limit. In order to describe the fluctuations around the mean field Hartree state, we introduce an auxiliary Hamiltonian on the N-particle space that is very similar to the one obtained from Bogoliubov theory. We show convergence of the auxiliary time evolution to the fully interacting dynamics in the norm of the N-particle space. The results will then be generalized to gases of large volume, i.e. the case where volume and density tend to infinity simultaneously. This is joint work with D. Mitrouskas, S. Petrat and a. Soffer.