Automatic signature verification on handheld devices can be seen as a means to improve usability in consumer applications and a way to reduce costs in corporate environments. It can be easily integrated in touchscreen devices, for example, as a part of combined handwriting and keypad-based multimodal interfaces. In the last few decades, several approaches to the problem of signature verification have been proposed. However, most research has been carried out considering signatures captured with digitizing tables, in which the quality of the captured data is much higher than in handheld devices. Signature verification on handheld devices represents a new scenario both for researchers and vendors. In this chapter, we introduce automatic signature verification as a component of multimodal interfaces; we analyze the applications and challenges of signature verification and overview available resources and research directions. A case study is also given, in which a state-of-the-art signature verification system adapted to handheld devices is presented.