This chapter gives an overview of mobile device’s hardware and software capabilities and their associated cellular networks. The overview summarizes general characteristics and, where useful, focuses on key features relevant to forensics. Developing an understanding of the components and organization of mobile devices (e.g., memory organization and its use) is a prerequisite to understanding the intricacies involved when dealing with them forensically. For example, mobile device memory that contains user data may be volatile (i.e., DRAM/SRAM) and require continuous power to maintain content similar to RAM in a personal computer. Similarly, the features of cellular networks are an important aspect of mobile device forensics since logs of usage, geographic location, and other data are maintained. Mobile device technologies and cellular networks are rapidly changing, with new technologies, products, and features being introduced regularly. Because of the fast pace with which mobile device technologies are evolving, this discussion captures a snapshot of the mobile device discipline at present.