The Dark Energy Survey (DES) has started mapping 5000 sq. deg. of the southern sky using DECam, a 570 mega-pixel optical and near-infrared camera with a large 3 sq. deg. field of view, set at the prime focus of the 4-meter Blanco telescope in CTIO, Chile. This will provide the collaboration with multi-band photometry of about 300 million galaxies to study dark energy using several probes.
In this talk I will introduce galaxy surveys in the context of observational cosmology, introduce the Dark Energy Survey and present some of its first results, including studies about photometric redshifts, weak lensing and large-scale structure of the universe.