The study of mesons and baryons which contain at least one charm quark is referred to as open charm physics. It offers the possibility to study up-type quark transitions. Since the q ̧uark can not be treated in any mass limit, theoretical predictions are difficult and experimental input is crucial. BESIII collected large data samples of e+e− collisions at several charm thresholds. The at-threshold decay topology offers special opportunities to study open charm decays.

In particlular, the model independent measurement of the strong phase between D0 and D0bar is unique to this production process. Furthermore, a search for direct CPV and the measurement of y_CP is presented.