Understanding the energy and matter content of the Universe and its evolution are key goals for the international astronomical community and all extremely large telescope projects. ELTs will bring a wide range of tools to bear on questions relating to the nature of dark energy and the formation and early evolution of galaxies. Natural seeing and ground-layer corrected instruments on ELTs will quantify the assembly of galaxies at modest redshifts, while near-IR diffraction-limited instruments will probe the internal structure of early galaxies and the epoch of first light and reionization.