A new generation of gigantic galaxy surveys is starting, in the overall quest to uncover the nature of dark matter and dark energy, the mysterious ingredients dominating the highly successful standard model of cosmology. Among these, the ESA Euclid satellite stands out as the most comprehensive endeavour, tackling the intertwined nature of gravity and the dark sector through precision measurements of cosmic expansion and structure growth. In my talk, I will present an overview of Euclid and its scientific goals, a few days before launch, scheduled for the first days of July from Cape Canaveral using a SpaceX Falcon-9 rocket. Euclid will spend six years mapping the galaxy and dark-matter distribution over one-third of the extragalactic sky. Photometry in the visible and infrared bands will provide approximate distances and shapes for more than two billion galaxies, while infrared spectroscopy will yield redshifts and more precise distances for more than 30 millions of them. Measurements of the cosmic expansion rate and the growth of structure will be extracted from these observations using two complementary cosmological probes: galaxy clustering and weak gravitational lensing. More broadly, the legacy of Euclid will impact virtually every area of extragalactic astrophysics and cosmology, providing a playground of unprecedented statistical power for generations of scientists to come. As such, Euclid most exciting results may well be those we cannot even imagine right now, as it always happened in the history of large galaxy surveys.