Abstract

We review the observational foundations of the ΛCDMΛCDM model, considered by most cosmologists as the standard model of cosmology. The Cosmological Principle, a key assumption of the model is shown to be verified with increasing accuracy. The fact that the Universe seems to have expanded from a hot and dense past is supported by many independent probes . The explosion of detailed observations in the last few decades has allowed for precise measurements of the cosmological parameters within Friedman–Lemaître–Robertson–Walker cosmologies leading to the ΛCDMΛCDM model: an apparently flat Universe, dominated by a cosmological constant, whose matter component is dominantly dark. We describe and discuss the various observational probes that led to this conclusion and conclude that the ΛCDMΛCDM model, although leaving a number of open questions concerning the deep nature of the constituents of the Universe, provides the best theoretical framework to explain the observations