An adaptive nonlinear control framework for multi-master/multi-slave teleoperation is proposed. A fully connected communication architecture is considered, which allows for transmission of position and force information between all master and slave robots. The operators are presented with a virtual intervening tool in order to collaboratively interact with the task environment. Models of operators, master and slave robots, tool, and environment are incorporated in the design. The performance and stability of cooperative teleoperation are guaranteed under dynamic interactions between slave robots and in the presence of model uncertainty. The robustness of the control system with respect to communication latency is also analyzed. Experimental studies demonstrate that the proposed approach is highly effective in all phases of a teleoperation task, i.e. in free motion and in contact with both flexible and rigid environments