The emergence of wireless and mobile networks has made possible the introduction of electronic commerce to a new application and research area: mobile commerce. Internet-enabled mobile handheld devices are one of the core components of a mobile commerce system, making it possible for mobile users to directly interact with mobile commerce applications. Much of a mobile user’s first impression of the application will be formed by his or her interaction with the device, therefore the success of mobile commerce applications is greatly dependent on how easy they are to use. This article first explains the role of handheld devices in mobile commerce systems and then discusses the devices in detail. A mobile handheld device includes six major components: i) a mobile operating system, ii) a mobile central processor unit, iii) a microbrowser, iv) input/output devices, v) a memory, and vi) batteries. Each component is described in detail and major products and technologies for the component are given. The technology needed for synchronization with desktop PCs and various mobile commerce applications is also presented.