Modern theories of cosmology assume that the Universe underwent a period of exponential expansion ("inflation") at an early stage. Inflation does not only solve some of the conceptual problems of earlier cosmological models, but also allows a causal explanation of structure formation. Moreover, it necessarily predicts the creation of gravitons, the spin-2 particles associated with the quantized gravitational field. In March 2014, the south-pole experiment Bicep2 announced the observational confirmation of such primordial gravitons. If true, this would constitute a major step towards an understanding of quantum gravity and the origin of our Universe. In my talk, I shall summarize the physics that is needed to understand this result, review the observations, and give an outlook on future developments.