  Measurements of single top quark production are presented, performed using
CMS data collected in 2011 and 2012 at centre-of-mass energies of 7 and 8 TeV.
The cross sections for the electroweak production of single top quarks in the
t-channel and in association with W-bosons is measured and the results are used
to place constraints on the CKM matrix element |V_tb|.
