Bill Moggridge has been an industrial designer for 40 years. In 1979, he designed what many call the first laptop computer: the GRiD Compass, which was used by businesspeople as well as by NASA and the U.S. military. The Compass established the language of laptop design: hinged closure, flat display, low-profile keyboard, and metal housing. In 1991, Moggridge cofounded Ideo, a design consultancy based in Palo Alto, CA. He is the founder of a movement known as "interaction design," which aims to do for the virtual world what industrial design does for the physical. In the recently published book Designing Interactions, he interviews 42 influential designers.

Technology Review: You say that at the beginning of any design, two things matter most: people and prototypes. Why?