Well-designed and usable interfaces for mobile commerce applications are critical. But given the uniqueness of the wireless environment, usability becomes even harder to ensure. This chapter describes the benefits and limitations of various wireless device interface technologies. It provides guidance on determining the usability of wireless devices, emphasizing the fact that context will factor heavily into the use of mobile applications. Some of the additional challenges that developers face when designing applications for wireless devices, such as infrastructure and software issues, are also discussed.