  We review results on rare and forbidden decays of D^0, D^+, and D^+_s mesons
from experiments at FNAL. The decay modes studied have two leptons in the final
state and, if observed, would constitute evidence for flavor-changing
neutral-current, lepton-flavor-violating, or lepton-number-violating processes.
To date, no evidence for these decays has been observed and upper limits are
obtained for their branching fractions. These limits can constrain various
extensions to the Standard Model. We present new upper limits from FNAL E791 on
the branching fractions for more than two dozen three- and four-body decay
modes.
