4+1 is a model designed by Philippe Kruchten to "describe the architecture of software systems, based on the use of multiple concurrent views".[1]​

[2]​ Views usually describe the system from the point of view of different stakeholders, such as end users, developers or project managers. The four views of the model are: logical view, development view, process view and physical view. Additionally, a selection of use cases or scenarios is often used to illustrate the architecture, serving as another view. Therefore the model contains 4+1 views:[1]​.