The ways in which cells obtain energy, use external nutrients, and make the constituents of macromolecules are at the heart of biology and medicine. The basics of these processes---intermediary metabolism---are similar from bacteria to multicellular organisms, and much of what is known about them comes from the eukaryotic microbe baker's yeast, Saccharomyces cerevisiae. This book explains intermediary metabolism, with examples primarily from yeast research. It covers central metabolic pathways; catabolism; fermentation; respiration; biosynthesis of small molecules, including cofactors and lipids; transport and compartments; storage molecules; the analysis of metabolism; and aspects of inorganic ion metabolism, stress, and metabolic toxicities. The book addresses the field's history and identifies areas where knowledge is thin. It can be used as a handbook for yeast specialists or as a systematic elementary text. The author is at Harvard Medical School.