I will discuss dark matter models, which in addition to a new stable particle introduce a new mediator with a mass comparable to or even below the dark matter mass. The crucial observation is that such a mediator will also induce new interactions between SM states, thus leading to a wide range of interesting signatures. For GeV-scale mediators, strong constraints arise from flavour physics and searches for rare constraints and I will consider the resulting dark matter phenomenology in the context of light pseudoscalars. The LHC, on the other hand, can achieve a unique sensitivity for TeV-scale mediators by combining searches for monojets and for dijet resonances. I will illustrate the remarkable complementarity of different dark matter probes using the example of an axial-vector mediator.