Multilateral systems involving haptic information sharing between several users have recently found interesting applications in cooperative haptic teleoperation and haptic-assisted training. It is intuitively understood that some tasks are performed more effectively with two hands or through collaboration than one hand or individual operation. By using multiple user interfaces (“masters”) and one remote robot (“slave”) or more, multilateral tele-cooperation systems enable haptic information sharing and collaboration in performing a task in a remote environment between multiple users. Despite the aforementioned benefits, research in this area is still in its initial stage. In fact, the only multilateral system that has been thoroughly investigated is the most basic one: the bilateral teleoperation system involving teleoperation between one master and one slave. As with any other robotic system, stability of multilateral haptic teleoperation systems is of paramount importance. Study of stability of such systems must consider the fact that the human users are part of the closed-loop system and thus affect the stability. However, to model the human operator is practically impossible, imposing great difficulties in the system’s stability analysis. This thesis presents a novel criterion to study the stability of multilateral teleoperation systems based on passivity. This criterion provides researchers with an analytical, closed-form, necessary and sufficient condition to investigate the stability of multilateral haptic teleoperation systems. The thesis also proposes a numerical method for investigation of absolute stability of trilateral teleoperators.