This is a book review of Introduction to Cosmology by Barbara Ryden. Apart from a general update, this second edition has expanded discussions of relativity and dark energy and a new chapter on the role of baryonic matter in structure formation. As is appropriate for an introductory book of moderate length, coverage of a broad range of topics is necessarily lacking more-detailed discussions, but Ryden avoids oversimplification while covering all topics at about the same level, appropriate for an undergraduate course in cosmology, although the last two chapters on structure formation go somewhat beyond that. The book begins with fundamental observations (dark night sky, homogeneity and isotropy, redshift, etc.) and builds up the theory needed to explain them, starting with Newtonian physics and moving through relativity to model universes based on the Robertson–Walker metric with various combinations of matter, radiation, curvature, and the cosmological constant. Those are followed by a discussion of classical observational cosmology before more-modern topics such as dark matter, CMB anisotropies, nucleosynthesis, inflation, and structure formation are covered. The mixture of narrative and equations is very close to a lecture course, and the book is well written. Complicated topics such as cosmological distances and horizons are presented briefly, but correctly.