Group theory is the branch of mathematics that studies symmetry, found in crystals, art, architecture, music, and many other contexts. Its beauty is often lost on students because it is typically taught in a technical style that is difficult to understand.
Visual Group Theory assumes only a high school mathematics background and covers a typical undergraduate course in group theory from a thoroughly visual perspective. Its more than 300 illustrations cover groups, subgroups, homomorphisms, products, quotients, Sylow theory, and a preview of Galois theory. Group Explorer, optional accompanying software, is available free online.
Visual Group Theory is published in the MAA's Classroom Resource Materials series, and won that organization's Beckenbach Book Prize. Sample materials from the book are available from the links above. Supplementary material is gradually appearing on this website, including the (extremely infrequently updated) Visual Group Theory Podcast.