  This paper reports a measurement of the W+b-jets production cross-section in
proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC. These
results are based on data corresponding to an integrated luminosity of 4.6
fb-1, collected with the ATLAS detector. Cross-sections are presented as a
function of jet multiplicity and of the transverse momentum of the leading
b-jet for both the muon and electron decay modes of the W boson. The W+b-jets
cross-section, corrected for all known detector effects, is quoted in a limited
kinematic range, using jets reconstructed with the anti-k_t clustering
algorithm with transverse momentum above 25 GeV and rapidity within +/- 2.1.
Combining the muon and electron channels, the fiducial cross-section for
W+b-jets is measured to be 7.1 +/- 0.5 (stat) +/- 1.4 (syst) pb, consistent
with next-to-leading order QCD calculations within 1.5 standard deviations.
