Connectivity between vehicles and between vehicles and the road infrastructure is the technological basis for “cooperative intelligent transportation systems”. The ability of a vehicle to communicate with its surroundings (other vehicles, the road infrastructure, or traffic control centers), generally referred to as vehicle-to-X (V2X) communicationVehicle-to-X (V2X) communication, makes it possible to provide many new or improved functions that lead to increased road safety, improved traffic efficiency, and greater personal comfort and convenience. Current developments are aimed in particular at supporting automated driving through the coordination of cooperative automated driving maneuvers. After a brief introduction, this chapter will first look at the necessary standardization activities for V2X systems. This will then be followed by a consideration of the different classes of use cases that have been conceived for a phased rollout, and examples will be provided. Next, the underlying system concept with its various subsystems, their functionality, and their interaction with one another will be explained. The essential basis for V2X systems is connectivity of the vehicles. A key element is therefore the specification of the data transmission technologies. After an overview of the V2X communication technologiesV2X communication technologies, the chapter will then go into the technical challenges, followed by a consideration of the radio channel and frequency allocation as well as a portrayal of the data formats needed for information exchange. Afterwards, the important questions of data security and data protection will be addressed, including an explanation of the aims and challenges of protection, followed by a portrayal of current solutions and their mechanisms. Finally, the chapter will look at the current status of market rollout and will provide a brief outlook on further developments.