  A measurement is presented of the associated production of a single top quark
and a W boson in proton-proton collisions at $\sqrt{s}=$ 13 TeV by the CMS
Collaboration at the CERN LHC. The data collected corresponds to an integrated
luminosity of 35.9 fb$^{-1}$. The measurement is performed using events with
one electron and one muon in the final state along with at least one jet
originated from a bottom quark. A multivariate discriminant, exploiting the
kinematic properties of the events, is used to separate the signal from the
dominant $\mathrm{t\overline{t}}$ background. The measured cross section of
63.1 $\pm$ 1.8 (stat) $\pm$ 6.4 (syst) $\pm$ 2.1 (lumi) pb is in agreement with
the standard model expectation.
