  The analysis of 60 1/pb data collected on the psi(3770) resonance with the
CLEO-c detector has produced the first statistically significant signal for D+
-> mu+ nu decay and led to the measurement of the decay branching fraction B(D+
-> mu+ nu) = (3.5 +- 1.4 +- 0.6) x 10-4 and the pseudoscalar decay constant f_D
= (202 +- 41 +- 17) MeV.
