Double parton scattering is investigated in proton-proton collisions at (\sqrt{s}) = 7 TeV where the final state includes a W boson, which decays into a muon and a neutrino, and two jets. The data sample corresponds to an integrated luminosity of 5 fb⁻¹, collected with the CMS detector at the LHC. Observables sensitive to double parton scattering are investigated after being corrected for detector effects and selection efficiencies. The fraction of W + 2-jet events due to double parton scattering is measured to be 0. 055 ± 0. 002 (stat. ) ± 0. 014 (syst. ). The effective cross section, σ eff, characterizing the effective transverse area of hard partonic interactions in collisions between protons is measured to be 20. 7 ± 0. 8(stat. ) ± 6. 6(syst. )mb.