Although hand-based interaction dominates mobile applications, this can be unsuitable for use by motor-impaired individuals or in situations such as musical performance or surgery, where the hands are otherwise occupied. The alternative of foot-based interaction, the subject of this chapter, has been shown to offer reasonable performance in such conditions and offers benefits in terms of diversity of input techniques, wide applicability, and social acceptability. This chapter also describes potential applications of foot-based interfaces, with an emphasis on factors related to usability. We aim to inspire designers and developers to consider the potential for leveraging interaction through the feet as a replacement for, or complement to, more traditional application designs.