Transportation systems are evolving in order to become safer, more efficient and increasing user quality of experience. Transportation infrastructure, vehicles and users are called to interact within vehicular context-aware environments termed as intelligent transportation systems (ITS). In this chapter, we will describe the fundamentals of ITS, and more specifically, the characteristics of vehicular communications in terms of the different types of communication links, systems and architectures employed. An overview of propagation standards as well as applications within multiple ITS domains is also given, as examples of a wide range of future developments to be seen.