Interoperability has been a requirement in NATO ever since the Alliance came into being - an obvious requirement when 16 independent Nations agree to allocate national resources for the achievement of a common goal: to maintain peace. With the appearance of data processing in the command and control pro­ cess of the armed forces, the requirement for interoperability expanded into the data processing field. Although problems of procedural and operational interoperability had been constantly resolved to some extent as they arose over the years, the introduction of data proces­ sing increased the problems of technical interoperability. The increase was partially due to the natural desire of nations to support their own national industries. But it was definetely also due to the lack of time and resources needed to solve the problems. During the mid- and late -1970s the International Standards Organisa­ tion (ISO) decided to develop a concept ("model") which would allow "systems" to intercommunicate. The famous ISO 7-layer model for Open Systems Interconnection (OSI) was born. The OSI model was adopted by NATO in 1983 as thi basis for standardization of data communications in NATO. The very successful (first) Symposium on Interoperability of ADP Sys­ tems, held in November 1982 at the SHAPE Technical Centre (STC), gave an exten~ive overview of the work carried out on the lower layers of the model and revealed some intriguing ideas about the upper layers. The first Symposium accurately reflected the state-of-the-art at that point in time.