For improving quality and safety of patient's care, for keeping the costs of health services, but also for successfully managing public health communication and cooperation between all stakeholders is inevitable. Such interoperability can be provided at different levels from simple data exchange up to business interoperability. The paper introduces those interoperability levels and international standards specifying and facilitating them. In that context, the expression of business requirements by domain analysis models or story boards as well as by functional models of the core applications enabling interoperability like EHR systems have been tackled. The role of decision support systems and infrastructural services has been considered as well.