This thesis presents a Virtual Reality (VR) system specifically designed to assist architects in the early stages of the design process. Modern CAD packages are designed for the detail design and construction stages and are not suitable for the creative work typical of the early conceptual process. The use of Virtual Reality systems promotes efficient real-time exploration of design proposals and modern Virtual Reality Aided Design (VRAD) systems allow users to create and manipulate 3D-shapes within the virtual environment and to experiment rapidly with different design solutions. Further, the development of desktop-based VR systems contributes towards the potential use of this technology in everyday practice The goal of this thesis is the development of a framework for a VR-based collaborative environment. This thesis, together with its companion research (Ucelli, 2002), describes the details of the working prototype called JCAD-VR (JavaTM Collaborative Architectural Design tool in Virtual Reality). JCAD-VR has been designed to provide the user with an effective tool to create basic geometries in a quick and simple way by using mouse commands without the need to type in values. This provides a significant level of abstraction over the rigid mathematical representation that is typical of traditional CAD systems. This work presents a description of the technical solutions tested during the development of JCAD-VR and in particular it focuses on the interaction techniques used for the implementation of its user-friendly Human-Computer Interface. Finally, the last part of this work gives the results of an experiment carried out to test the capabilities of the system in a possible scenario. This shows that JCAD-VR, even at prototype level, could be used as an effective tool to create and share design ideas among members of a design team.