Relay feedback has attracted considerable research attention for more than a century but there has been no recent summary of the many newly-developed tools and results now available for this important area as a whole, those that have been published tending to focus on one process or controller type only. Relay Feedback is divided into three parts, the first of which is devoted to the analysis of relay feedback systems within a general setting with information on: existence of solutions; existence of limit cycles; local and global stability of limit cycles; limit cycles with more than two...