Abstract : It is now well established that a large part of the matter in the Universe is some substance which appears to be oblivious to any force but gravity. The nature of this dark matter remains a mystery. Could it be a new particle, as light as an electron, or might it be made of black holes as massive as many Suns? In this talk, I will first illustrate how precise measurements of the frequency spectrum and angular fluctuations of the cosmic microwave background (CMB) can help shed light on the nature and properties of dark matter. Specifically, I will discuss CMB tests of feeble dark matter interactions with photons, electrons and nuclei, as well as the signatures of accreting primordial black holes as a potential dark matter candidate.