3D objects are increasingly being used in a very wide range of areas. The use of patient reconstructed models in medecine is becoming frequent. However, tools allowing users to interact with complex 3D objects are rudimentary. In the last past years, many experiments have improved immersive virtual environments, especially concerning visual representation. However, a lot of work remains to improve interactive devices used in such environments. At the same time, the need for cooperation around 3D models has increased. Our research goals are to propose interaction models that apply to 3D complex virtual objects and to experiment them on two applicative themes : surgery simulation and collaborative virtual environments.