Donald G. York is the Horace B. Horton Professor of Astronomy and Astrophysics at the University of Chicago. An observational cosmologist, he has focused much of his research on the gas and dust between galaxies for the clues they provide to the formation and evolution of the universe. He was the founding director of the Apache Point Observatory in Sunspot, New Mexico, serving for fourteen years, and of the Sloan Digital Sky Survey, one of the most ambitious collaborative projects ever undertaken by astronomers. He is also the founder and co-director of the Chicago Public Schools/University of Chicago Internet Project. A graduate of the Massachusetts Institute of Technology, Dr. York took his Ph.D. in astronomy and astrophysics at Chicago in 1971. For the next eight years, he worked on ultraviolet spectra of the interstellar medium as a research astronomer. Named a senior research astronomer at Princeton in 1979, he accepted an associate professorship in astronomy and astrophysics at Chicago three years later. Promoted to professor in 1985, he was awarded his present chair in 1992. Dr. York has lectured on his research throughout the United States as well as in Australia, Canada, China, Japan, Russia, Italy, Germany, France, and England. As a Harlow Shapley Lecturer of the American Astronomical Society, he lectures at small colleges across America on cosmology and on science and religion. He is the author of some 330 scientific papers.