Pioneering University of Chicago cosmologist Michael S. Turner focuses his remarks on “the Chicago School of Cosmology,” from Edwin Hubble and George Ellery Hale to the present. Hubble, SB 1910, PhD 1917, discovered that the universe consists of billions of galaxies and that it has been expanding since it began in a big bang. Hale was the first chairman of the University’s Department of Astronomy and Astrophysics. He also founded Yerkes Observatory, which under his leadership developed the big reflecting telescopes that are the workhorses of optical astronomy today, making discoveries from the expanding universe to planets orbiting other stars.Turning to more recent times, Turner discusses efforts that started in the 1980s at UChicago to establish the new field of particle astrophysics and cosmology. At that time, the Chicago School, consisting primarily of the late David Schramm, Edward "Rocky" Kolb, the Arthur Holly Compton Distinguished Service Professor in Astronomy and Astrophysics, and Turner, was alone in pushing this idea. “Today this idea that there are deep connections between the very big and the very small is universally accepted, has propelled the field to its current prominence, and underpins our understanding of the universe,” Turner said. “As we say at Chicago, ideas matter!”The Ryerson Lecture grew out of a 1972 bequest to the University by Nora and Edward L. Ryerson, a former chairman of the board of trustees. The lecture honors excellence in academic pursuits. A faculty committee selects the Ryerson Lecturer based on research contributions of lasting significance.