We describe a new multi-robot system, named SWARM-BOTS, that exploits physical inter-connections to solve tasks that are impossible for a single robot. This is for instance the case of passing large gaps or high steps in all-terrain conditions. In order to achieve this type of autonomous collective operations, the design of the type of connection, as well as its sensors and actuators, plays a key role. This paper presents the choices made in the SWARM-BOTS project and the know-how collected until now. The requirements for autonomous operation and mobility of each robots have led to the development of a connectivity very different those found in selfrecon gurable robots. Some of the solutions employed for this problem are inspired upon physical connectivity of social insects. We also illustrate with two experiments how sensors and actuators allow autonomous operation in connection, release as well as passive and active exploitation of inter-robot degrees of freedom (DOF).