A functional software architecture (FSA) is an architectural model that identifies enterprise functions, interactions and corresponding IT needs. These functions can be used as a reference by different domain experts to develop IT-systems as part of a co-operative information-driven enterprise. In this way, both software engineers and enterprise architects can create an information-driven, integrated organizational environment. Overview When an integrated software system needs to be developed and implemented several tasks and corresponding responsibilities can normally be divided: Strategic management and business consultants set objectives in relation to a more efficient/effective business process. Enterprise engineers come up with a design of a more efficient business process and a request for a certain information system in the form of an Enterprise Architecture. Software engineers come up with the design of this information system, which describes the components and structural features of the system by use of a certain architecture description language (ADL). Computer programmers code the different modules and actually implement the system. The described work division is in reality much more complex and also involves more actors but it outlines the involvement of people with different backgrounds in creating a software system that enables the organization to reach business objectives. A wide variety of material produced by different actors within this system development process needs to be exchanged between, and understood by, multiple actors. Especially in the field of software engineering many tools (A4 Tool, CAME, ARIS), languages (ACME, Rapide, UML) and methods (DSDM, RUP, ISPL) are developed and extensively used. Also, the transition between the software engineers (step 3) and computer programmers (step 4) is already highly formalized by, for instance, object-oriented development. Setting strategic objectives (step 1) and the corresponding search for business opportunities and weaknesses is a subject extensively discussed and investigated for more than a hundred years. Concepts like business process reengineering, product software market analysis, and requirements analysis are commonly known and extensively used in this context. These strategic inputs must be used for the development of a good enterprise design (step 2), which can then be used for software design and implementation respectively. Recent studies have shown that these enterprise architectures can be developed by several different methods and techniques. Before these methods and techniques are discussed in detail a definition of an enterprise architecture is given: An Enterprise Architecture is a strategic information asset base, which defines the mission, the information necessary to perform