The emergence of wireless and mobile networks has made possible the introduction of electronic commerce to a new application and research subject: mobile commerce. Mobile commerce is a promising trend of commerce because Internet-enabled smartphones such as iPhones are becoming very popular these days. People use smartphones to perform daily tasks like browsing the mobile Internet and making phone calls anytime and anywhere. However, understanding or constructing a mobile or an electronic commerce system is not easy because the system involves a wide variety of disciplines and technologies and the technologies are constantly changed. To facilitate understanding and constructing such a system, this chapter divides the system into six components: (i) applications, (ii) client devices or computers, (iii) mobile middleware, (iv) wireless networks, (v) wired networks, and (vi) host computers. Elements in these components specifically related to the subject are described in detail and lists of current technologies for component construction are discussed.