During the last decade, cosmology has entered a precision era, leading to the prevalence of the standard cosmological model, ΛCDM. Nevertheless, the main ingredient of this model, dark energy, remains mysterious while dominating the energy budget of the Universe. Its comprehension is the current Graal of this domain. The next generation of cosmological surveys, among which Legacy Survey of Space and Time (LSST) of the Vera Rubin Observatory (on the ground) & Euclid (in space), both starting in 2022, are in that regard the most important projects for the next 10 years. 

Models predict that clusters of galaxies assemble from mergers of galaxy groups at z>1.5-2. The detections and observation of clusters and proto-clusters at these epochs put strong constraints on galaxy formation and quenching, and on the cosmological model.