This article focuses on the interoperability feature seen as a specific requirement. Indeed, any complex system (e.g. a train, an organisation or an IT system) need to interact with other systems, thereby forming a heterogeneous environment. All these systems are not necessarily designed to function properly and efficiently with one another, whether from a conceptual, technical, behavioural or organizational standpoint. This paper highlights what seems to be relevant in terms of conceptual definitions and modelling framework whenever a (group) of engineer(s) intends to design what we call here a “natively interoperable system” or, at least, a system maximizing its interoperability capabilities. To proceed, as a first prerequisite, a definition of the concept of interoperability is here proposed for complex system engineering. The second prerequisite consists of establishing the needs of a design team assigned to design such “natively interoperable system”. An interface pattern model with sufficient generic, formal and pragmatic qualities is then proposed and illustrated briefly.