Information systems of a modern hospital govern extremely important functions as patient management, control of work flows, administration etc. However a great variety of recommended standards are used while in most cases no effective coordination and intercommunication is possible. Some years ago to simplify and resolve this problem IHE was created; it is a technical framework which identifies a number of components of the healthcare enterprise (the "actors") whose interactions are defined in terms of "transactions", that should be implemented according to HL7 and DICOM standards. Attempting an in-depth understanding of IHE structure and its principles of function, those transactions that can occur among the various actors, which of these are supported and which require specific actors, are analyzed. IHE is continuously evolving, therefore open to the factual contribution of all health professionals who can point out the main instances that emerge daily from their activity in the field. While its origin was specific for the field of radiology, the true soul and driving force of the project lay on the type of approach used: to get together medical specialists and information technology professionals in order to identify and solve the difficulties which hindered an effective and functional integration of healthcare information systems.