A measurement of the H → ττ signal strength is performed using events recordedin proton-proton collisions by the CMS experiment at the LHC in 2016 at a center-of-mass energy of 13 TeV. The data set corresponds to an integrated luminosity of35.9 fb−1. The H → ττ signal is established with a significance of 4.9 standard devia-tions, to be compared to an expected significance of 4.7 standard deviations. The bestfit of the product of the observed H to tautau signal production cross section and branch-ing fraction is 1.09+0.27 times the standard model expectation. The combination with −0.26the corresponding measurement performed with data collected by the CMS experiment at center-of-mass energies of 7 and 8 TeV leads to an observed significance of 5.9 standard deviations, equal to the expected significance. This is the first observation of Higgs boson decays to τ leptons by a single experiment.'njets', 'nbjets','mt', 'mjj', 'dEtajj', 'hjj_pT', 'higgs_pT'