For two decades, extraordinary effort has been devoted to clarifying the controversial results in direct dark matter detection. The claim of DAMA/LIBRA for a dark matter annual modulation signal is in apparent contradiction with most of the results of the other direct detection experiments, but a material-independent check of this signal can still be decisive. For this reason, COSINUS aims to develop a sodium iodide-based cryogenic scintillating calorimeter, whose two-channel readout of light and phonon allows an event-by-event discrimination of the dominant β/γ-background from the sought-for nuclear recoils