Stephen Wolfram was born in England in 1959. He was educated at Eton and Oxford, and received his Ph.D. in theoretical physics from Caltech at the age of twenty. Wolfram's early work in particle physics, cosmology and computer science earned him one of the first MacArthur awards. Wolfram began his work on the problem of complexity in 1981. And after writing the sequence of papers collected in this book, Wolfram founded the first research centre and the first journal devoted to the study of complexity. Then in 1986, he formed Wolfram Research, Inc., and began the development of Mathematica. Released in 1988, Mathematica has become the standard software system for technical computation used by scientists, engineers, students and others around the world. Wolfram has been the recipient of many awards for science and business. He now divides his time between basic research and the leadership of his company.