This book incorporates data rate issues that arise in control design for systems involving communication networks. The general setup is that, given a plant, a communication channel with limited data rate and control objectives, one must find a controller that uses the channel in the feedback loop to achieve the control objectives. The theoretical question of interest is to find the minimum data rate necessary for the channel. This book is motivated by the recent developments in communication technology and aims at engineers and scientists in this field. The use of networks has become common practice in many control applications connecting sensors/actuators to controllers. The book therefore provides the fundamentals of the networks used in control systems, based on hybrid systems theory. The book focuses on the use of networks in distributed systems and on quantization in messages sent over networks.