As financial integration proceeds, new issues are coming up in the field of supervision of financial markets. Some have to do with better cooperation among supervisors whether in the same field or on across-sectoral basis. The possibility to cooperate is however restricted by the public nature of most supervisors: public authorities should exercise their powers themselves, and risks should be borne by the legally empowered supervisor. In order to make supervision more effective, cross border delegation is needed. However, it is unclear to what extent supervisors can delegate, tasks as well as competences or decisions. This paper aims to give a first overview of the issues to be tackled including an attempt to analyse the liability question.