The paper presents a new general principle of administrative law regulated in art. 7b of the Code of Administrative Proceedings. Hitherto, a collaboration of administrative bodies was one of the institutions of the administrative proceedings, that allowed to take a position before a final decision. The new principle expands the scope of the notion of cooperation for another procedural expressions of collaboration between administration bodies. It orders e.g. using adequate measures, taking into account the character, circumstances, and degree of the complexity of the matter.