Systems architecture is the purposeful, goal-oriented fundamental organization of technical systems. It defines the inner structure of these systems by means of components, interfaces between these components, and interfaces to the outside world. Systems architecture enables desired behavior and impedes undesired behavior by purposefully composing elementary functionality.

The architecture of a system is described in terms of models, in both semi-formal and natural language; e.g., via SysML diagrams, block diagrams or plain text. Given the nature of complex systems, there typically does not exist one all-encompassing system model, but a series of descriptions from multiple viewpoints – such as structure, behavior, data, and performance.

Systems architecture is a creative process, on the basis of knowledge, experience, communication and novel insights. Therefore, systems architecture cannot be automated nor reduced to systematically applying a prescribed set of methods and transformations according to some process model. However, there do exist architecture frameworks, like TOGAF, to ensure that all relevant aspects of a given architectural problem are taken care of and to foster consistency among the different system models created. Architecture frameworks combine and bundle experience, patterns and best-practices.