Abstract. In this paper we propose viewing Virtual Worlds as open Multiagent Systems and propose the 3D Electronic Institutions methodology for their development. 3D Electronic Institutions are Virtual Worlds with normative regulation of interactions. More precisely, the methodology we propose here helps in separating the development of Virtual Worlds based on the concept of 3D Electronic Institutions into two independent phases: specification of the institutional rules and design of the 3D interaction environment. The new methodology is supplied with a set of graphical tools that support the development process on every level, from specification to deployment. The resulting system facilitates the direct integration of humans into Multi-Agent Systems as they participate by driving an avatar in the generated 3D environment and interacting with other humans or software agents, while the institution ensures the validity of their interactions. 1