The enzymes that catalyze the synthesis and degradation of oligo‐ and polysaccharides are among the most important in the biosphere, because of the key role they play in the global carbon cycle. Thanks to a long and rich history of scientific study, the catalytic mechanisms of the glycoside hydrolases and transglycosylases are generally well understood in terms of enzyme‐substrate interactions and transition state structure. Recent structure‐function studies of polysaccharide lyases have also begun to unravel the secrets of catalysis in these distinct classes of carbohydrate‐active enzymes. Built upon a firm understanding of enzyme structure and mechanism, an impressive number of technological applications highlight the prowess of these biological catalysts.