The successful deployment and worldwide acceptance of the second-generation (2G) mobile telecommunication systems combined with the need for more advanced and ubiquitous mobile services have paved the way to the initiative of the so-called third-generation (3G) mobile telecommunication systems. In this chapter, we will discuss the network architecture of 3G systems, i.e. we will describe how the network is built, what functional elements exist, what overall functionality is provided, etc.