Using lattice gauge theory in the quenched approximation we calculate the decay constants and second moments of wave functions of pseudoscalar mesons containing nonstrange, strange, and charmed quarks. We find f/sub D/ = 134(23) MeV and f/sub D//sub >//sub s/ = 157(11) MeV. We use the methodology of two recent computations of the second moment of the pion wave function, and find that a nonperturbative treatment of operator mixing gives results consistent with calculations using sum rules.