What is the phenomenon of occupation referred to in Article 2 common to the four Geneva Conventions of 1949? What are its specificities, factually and legally, distinguishing it from "classic" international armed conflict? The ambit of this chapter is to provide a clear response to these questions. It first defines the concept of occupation. It then highlights the main characteristics and rules underlying its regulation. Finally, it shows that, even though the concept and its legal framework might appear to be outdated, both are still relevant nowadays.