This book explains in clear, non-mathematical language the measurements and the interpretation of the resulting data that have led to the current understanding of the origin, evolution and properties of our expanding Big Bang universe. Theoretical concepts are emphasized, but no other book for the layman explains how model universes are generated, and how they function as the templates against which ours is compared and analyzed. Background material is provided in the first four chapters; the current picture and how it was attained are discussed in the next four chapters; and some unsolved problems and conjectured solutions are explored in the final chapter.