  I discuss hadronic decays of $D$ mesons with emphasis on the recent discovery
of charm CP violation in $D^0\to K^+K^-,\pi^+\pi^-$ decays. The measured
difference $\Delta a_{CP} \, \equiv \; a_{CP}^{\mathrm{dir}}(D^0\rightarrow
K^+K^-) - a_{CP}^{\mathrm{dir}}(D^0\rightarrow\pi^+\pi^-) = \; (-15.4\pm
2.9)\cdot 10^{-4}$ of two direct CP asymmetries exceeds the SM prediction by a
factor of 7. A possible explanation is an enhancement of the penguin amplitude
entering $ a_{CP}^{\mathrm{dir}}$ by QCD effects which are not understood yet.
Alternatively, $\Delta a_{CP}$ could be dominated by contributions from new
physics. In order to distinguish these two hypotheses further CP asymmetries
should be measured. To this end CP asymmetries resulting from the interference
of two tree-level amplitudes auch as $a_{CP}^{\mathrm{dir}}(D^0\rightarrow
K_SK_S)$ or $a_{CP}^{\mathrm{dir}}(D^0 \to K^{*0} K_S)$ are especially
interesting.
