This Technical Report entitled Interoperability of telehealth systems and networks — Part 1: Introduction and definitions includes a brief introduction to interoperability of telehealth systems and networks, along with definitions of telehealth and related terms. The scope of this document does not include the conformity and interoperability tests or functional specifications for telehealth systems and networks. A more detailed description of issues concerning the interoperability of telehealth systems and networks capable of operating in real-time mode (including audio, video, and data conferencing) is included in Part 2. Real-Time Systems. That document identifies standards for real-time telehealth systems, examines interoperability aspects of telehealth applications, and defines interoperability requirements for telehealth systems and networks. Other documents will describe the issues surrounding interoperability of telehealth systems that use store-and-forward and media streaming technologies. An informative annex describing the Telehealth Technical Reference Architecture has been also been included to describe more clearly the various components of a telehealth system and the elements that need to be addressed in formulating a set of requirements for these various components.