>Magister Scientiae - MSc / The growth of structure in the Universe proceeds via the collapse of dark matter and baryons. This process is retarded by dark energy which drives an accelerated expansion of the late Universe. In this thesis we use cosmological perturbation theory to investigate structure formation for a particular class of dark energy models, i.e. interacting dark energy models. In these models there is a non-gravitational interaction between dark energy and dark matter, which alters the standard evolution (with non-interacting dark energy) of the Universe. We consider a simple form of the interaction where the energy exchange in the background is proportional to the dark energy density. We analyse the background dynamics to uncover the e ect of the interaction. Then we develop the perturbation equations that govern the evolution of density perturbations, peculiar velocities and the gravitational potential. We carefully account for the complex nature of the perturbed interaction, in particular for the momentum transfer in the dark sector. This leads to two di erent types of model, where the momentum exchange vanishes either in the dark matter rest-frame or the dark energy rest-frame. The evolution equations for the perturbations are solved numerically, to show how structure formation is altered by the interaction.