This paper describes a novel form of navigation aid for mobile robots. It is suggested that a robot lay a heated trail to mark its path. This information about the robot trajectory can be used to assist a robot when it performs area coverage operations such as floor cleaning or allow a robot to follow the path previously taken by itself or another robot. Prototype devices for laying and tracking a heat trail are described and details of their performance are given. A mobile robot has been equipped to lay and track a heat trail.