The concept of boundary represents one of the fundamental philosophical issues triggered and required by the reflection upon geography – and ontology of geography specifically. But what kind of entity are geographical boundaries? What sorts of boundary have been identified by contemporary ontologists of geography? How can boundaries be classified from a geo-ontological point of view? What are the main contemporary classifications of geographical boundaries? How can culture and human beliefs influence such classifications? These questions represent the starting point of this paper, aimed at analyzing how the notion of boundary has been conceived by contemporary ontologists of geography, what kinds of geographical boundaries have been identif...