The current picture of our Universe has emerged from a remarkably successful combination of cosmological theory and a wide range of observations. After the discovery of an accelerated expansion of the late-time Universe from distant supernovae in 1998, independent observations of the cosmic microwave background and of the large-scale distribution of galaxies have supported and strengthened the overall picture.

In the standard cosmological model, normal baryonic matter contributes only roughly 5% to the overall density, the rest being in the form of dark matter (23%) and dark energy (72%). Whereas dark matter has already been postulated by Zwicky in 1933, the existence and dominance of dark energy was unexpected and raised fundamental questions as e.g. the range of validity of Einstein's gravity, the role of extra dimensions, the existence of new forces, the nature of vacuum, the relation to the inflationary field and to the particle physics models.