Quantum fluctuations in the very early Universe give rise to temperature and polarisation anisotropies in the cosmic microwave background, and seed present-day cosmic structures. Primordial gravitational waves generated by these fluctuations carry information about the energy scale of inflation, and they are weakly non-Gaussian. However, primordial gravitational waves can also be generated by other sources, and carry imprints of the energy content of the early Universe. Scientists at MPA recently showed that these gravitational waves can be highly non-Gaussian, with a skewness much larger than for those generated by vacuum fluctuations. They concluded that non-Gaussianity is thus an important test of the origin of primordial gravitational waves.