This chapter provides a survey on localization techniques for connected and automated vehicles (CAVs), and explores a new way of improving the accuracy of positioning of vehicles through collaboration. An autonomous vehicle can be defined as “a motor vehicle that uses artificial intelligence, sensors, and global positioning system coordinates to drive itself without the active intervention of a human operator”. Modern vehicles barely manage without sensors, and the sensors are getting smaller and lighter. With increasing distribution, they will become cheaper, so they can be installed in more and more vehicles. The ultrasound technology in vehicles is already mature, and the corresponding sensors are inexpensive and easy to use. Due to the propagation characteristics of sound, ultrasonic sensors work only at short distances and low speeds, for example, in self-parking and blind-spot detection. Radar, or radio detection and ranging, uses reflected radio waves to sense surrounding objects.