  This M.Sc. thesis describes a search for exotic leptons. The search has been
performed using data from the OPAL detector at the Large Electron Positron
collider at CERN. The total integrated luminosity was 663 pb$^{-1}$ with center
of mass energies in the range of 183-209 GeV. The work has been concentrated on
the study of production of heavy leptons via the charged current channel and
disintegration of the $W$ into two quarks. In particular, single production of
heavy leptons in the mass region 100-170 GeV has been extensively studied. No
evidence for any new particles has been found. The results translate into upper
limits on the mixing between the heavy and the ordinary lepton for different
heavy lepton masses. The limits on the mixing angles are generally improved in
comparison with the nominal value $\zeta^2\sim 0.005$.
