Résumé : Measurements of the differential and double-differential Drell–Yan cross sections in the dielectron and dimuon channels are presented. They are based on proton–proton collision data at √s = 8Tev recorded with the CMS detector at the LHC and corresponding to an integrated luminosity of 19.7 fb-1. The measured inclusive cross section in the Z peak region (60–120GeV), obtained from the combination of the dielectron and dimuon channels, is 1138 ± 8(exp) ± 25 (theo) ± 30 (lumi) pb, where the statistical uncertainty is negligible. The differential cross section dσ/dm in the dilepton mass range 15–2000 GeV is measured and corrected to the full phase space. The double-differential cross section d2σ/dmd