  We present the complete calculation of $W$-boson production in association
with a jet in hadronic collisions through next-to-next-to-leading order in
perturbative QCD. To cancel infrared divergences we introduce a new subtraction
method that exploits the fact that the $N$-jettiness event-shape variable fully
captures the singularity structure of QCD amplitudes with final-state partons.
This method holds for processes with an arbitrary number of jets, and is easily
implemented into existing frameworks for higher-order calculations. We present
initial phenomenological results for $W$+jet production at the LHC. The NNLO
corrections are small and lead to a significantly reduced theoretical error,
opening the door to precision measurements in the $W$+jet channel at the LHC.
