The airwaves are crammed with various mobile wireless services, ranging from mobile phone networks to wireless local area networks (LANs). There are many definitions of mobile commerce (m-commerce). One definition consists of all or part of mobile wireless services—the service provided by mobile phone systems, which has achieved huge success. Mobile phone users originate from all walks of life and include almost all age groups—from teenagers to retired people. It creates a new way of personal communication without location constraints. The number of active mobile phones grew tenfold in the period from 1996–2001, and the growth is still strong, despite the economic downturn. The number of active cell phones was around 946 million in 2001 (Shirky, 2002). In addition, each wireless service has unique technology. Instead of briefly describing all mobile wireless services, we will concentrate on the mobile phone and the PDA related to mobile telecommunication. M-commerce is, therefore, defined as e-commerce carried out in handheld devices, such as the mobile phone and PDA, through a mobile telecommunication network. The chapter is organized as follows. The first two sections introduce the main technologies—the mobile telecommunication network and the wireless protocols, where the challenges for m-commerce are investigated. Then m-commerce applications are discussed. Finally, we will highlight the issues in implementing m-commerce.