This chapter will propose an ontology of virtual environments that calls into question the dichotomy between the real and the virtual. This will draw on the concepts of trajectivity and ‘médiance' in order to describe the way virtual environments, with their technological and symbolic features, take part in the construction of human environments. This theoretical proposition will be illustrated with the analysis of Arcadia, a virtual environment built in Second Life. Finally, a mesocriticism will be proposed as a new approach for the study of virtual environments.