  We have studied the leptonic decay D^+_s to tau^+ nu_tau, via the decay
channel tau^+ to e^+ nu_e anti-nu_tau, using a sample of tagged D_s^+ decays
collected near the D^*_s D_s peak production energy in e^+ e^- collisions with
the CLEO-c detector. We obtain
  B(D^+_s to tau^+ nu_tau) = (5.30 +- 0.47 +- 0.22) % and determine the decay
constant f_Ds = (252.5 +- 11.1 +- 5.2) MeV, where the first uncertainties are
statistical and the second are systematic.
