After the great success of already three generations of space missions dedicated to the study of the Cosmic Microwave Background, the basic picture of a global cosmological model has emerged, with main parameters such as expansion rate, density of various forms of matter and energy, and spatial curvature of the universe measured with precision of the order of a few per cent. However, many open questions remain. Whether a phase of cosmic inflation did indeed seed initial perturbations is not fully demonstrated, and the mechanisms that seeded inflation not well understood or constrained. Dark matter and dark energy, postulated to explain 96% of the energy density in the Universe, are of unknown nature and still lack confirmation by direct observations. I will review in what way future observations of the CMB, and in particular a future European space mission, can help further validate or challenge the model, and provide further constraints of the fundamental properties of matter and forces at energy scales ranging up to twelve orders of magnitude higher than those constrained at the LHC. For this very challenging task, it is required to design instruments with exceptional degrees of performance, a technological feat that will require observing the sky with thousands of multi-channel, multi-polarization detectors operating at 100mK in space, the properties of each of which must be calibrated to exquisite accuracy using the scientific data themselves to monitor contamination by systematic effects and astrophysical emission that can outshine by several orders of magnitude the tiny signals of interest to probe fundamental physics with CMB observations.
