CERN-LHC. The production cross section of a W boson in association with two b jets is measured using a sample of proton-proton collisions at $ \sqrt{s} = $ 8 TeV collected by the CMS experiment at the CERN LHC. The data sample corresponds to an integrated luminosity of 19.8 fb$^{-1}$. The W bosons are reconstructed via their leptonic decays, $ \mathrm{ W }\to\ell\nu $, where $\ell=\mu$ or $\mathrm{ e }$. The fiducial region studied contains exactly one lepton with transverse momentum $ p_{\mathrm{T}}^{\ell} > $ 30 GeV and pseudorapidity $ | {\eta^{\ell}} | < $ 2.1, with exactly two b jets with $ p_{\mathrm{T}} > $ 25 GeV and $ | {\eta} | < $ 2.4. The fiducial region excludes events with a second lepton, $p_{\mathrm{T}}^\ell > $ 10 GeV and $ | {\eta}^\ell | < $ 2.4, or a third jet with $ p_{\mathrm{T}} > $ 25 GeV and $ | {\eta} | < $ 4.7.