Measurements are presented of associated production of a W boson and a charm quark (W + c) in proton–proton collisions at a center-of-mass energy of 13Te. The data correspond to an integrated luminosity of 35.7fb-1 collected by the CMS experiment at the CERN LHC. The W bosons are identified by their decay into a muon and a neutrino. The charm quarks are tagged via the full reconstruction of D ∗ (2010) ± mesons that decay via D ∗ (2010) ± → D + π ± → K ∓ + π ± + π ± . A cross section is measured in the fiducial region defined by the muon transverse momentum pTμ>26Ge, muon pseudorapidity | η μ | < 2.4 , and charm quark transverse momentum pTc>5Ge. The inclusive cross section for this kinematic range is σ(W+c)=1026±31(stat)+76-72(syst) pb. The cross section is also measured differentially as a function of the pseudorapidity of the muon from the W boson decay. These measurements are compared with theoretical predictions and are used to probe the strange quark content of the proton.