Carbohydrates started to catch the interest of immunologists in the early 20th century. Vaccines based on bacterial polysaccharides were proven effective to prevent infections, but were overshadowed by antibiotics for a long time. When antibiotic resistances emerged, polysaccharide vaccines rapidly gained importance. However, infants were not protected from infectious disease by vaccines consisting of pure polysaccharides. Protein conjugates of bacterial saccharides were introduced to overcome this challenge. Glycoconjugate vaccines induce immunological memory against pathogens, even in infants, and have become standard in childhood vaccination schedules. Despite the effectiveness of glycoconjugate vaccines, isolation of natural pathogen-derived glycans is often tedious, and numerous measures of quality control have to be taken. Synthetic oligosaccharides facilitate glycoconjugate vaccine manufacturing and serve as tools for detailed mechanistic studies on vaccine immunology. Chapter 3 provides insight into the production, mechanisms of action, and future directions of carbohydrate-based vaccines.