There’s more to interfaces than what’s on the screen. While often overlooked, input deserves to be on equal footing with its more popular sibling, output. Also, input is a rare case where we can model user behavior mathematically. In this module, you’ll learn how good input is more than just preference, trace input from the fingertip to the screen, and think about the diversity of possible input devices and their relative merits.

We live in an information-rich world. Consequently, the hardest part of interaction is often finding what we want or finding something that we didn’t know what to ask for. From e-commerce to digital libraries, good search design is central to human-computer interaction in the 21st century.