John MacCormick is associate professor of computer science at Dickinson College and a leading teacher, researcher, and writer in his field. He has a PhD in computer vision from the University of Oxford and has worked in the research labs of Hewlett-Packard and Microsoft. His previous books include Nine Algorithms That Changed the Future: The Ingenious Ideas That Drive Today's Computers (Princeton). Erik Demaine and Martin Demaine created the curved crease sculpture featured on the cover of What Can Be Computed? Cover photo courtesy of the artists.