Twentieth-century and twenty-first-century elementary particle physics is full of quarks, leptons, antimatter, and dark energy. How is a reader supposed to understand physics when much of what he or she may, or may not, remember from high-school physics is no longer current? This alphabetically arranged guide is intended for a broad audience, including advanced high-school and college students as well as general readers. An international team of physicists contributed 153 entries, each with a bibliography of recommended books, journals, and Web sites. See also references appear at the end of each article. Also included are a reader's guide presenting a topical arrangement of entries, a time line, a glossary, and a list of common abbreviations and acronyms. Case studies of experiments such as the measurement of the muon, profiles of important laboratories such as Fermilab, and biographies of physicists such as Paul Dirac are among the entries, which are illustrated with tables, photograph, and schematics. Building Blocks of Matter is a supplement to the Macmillan Encyclopedia of Physics (1996). As such, it will help students understand the physics of elementary particles, that is, particles that cannot be broken down. Because of its focus, it is more specialized than a physics dictionary. Recommended for science reference collections in academic and public libraries, especially those that own the Macmillan Encyclopedia of Physics.