  Recently a lot of new experimental results on open charm hadrons have
appeared. In particular many D meson resonances have been discovered. We
discuss strong decays of positive and negative parity charmed mesons within
heavy meson chiral perturbation theory and study the impact of excited charm
states on the determination of the effective meson couplings. Motivated by
recent experimental results we also reconsider semileptonic D to P l nu and D
to V l nu decays within a model which combines heavy quark symmetry and
properties of the chiral Lagrangian. Using limits of soft collinear effective
theory and heavy quark effective theory we parametrize the semileptonic form
factors. We include excited charm meson states in our Lagrangians and determine
their impact on the charm meson semileptonic form factors. In some scenarios of
new physics an up-like heavy quark appears, which induces FCNC at tree level
for the c to u Z transitions. We investigate FCNC effects in D rare decays in
particular the c to u l+ l- transition which might occur in D+ to pi+ l+ l- and
D0 to rho0 l+ l-.
