Our current picture of how galaxies evolve leans heavily on the work of Sidney van den Bergh. He has directed his observational studies to critical aspects of galaxy evolution. He discovered the ‘G dwarf’ problem that there are far fewer metal-poor stars that would be expected from simple theories of galactic evolution. His studies of the chemical abundances of supernova remnants have given direct evidence that the interstellar gas is being enriched in metals by these events. The photometric system he introduced is well adapted to determine the chemical and physical properties of stars. Using the 200-inch Palomar telescope, he made the pioneering study of the globular cluster system of the Andromeda galaxy and deduced that these clusters were systematically more metal-rich than those around our galaxy. He has catalogued and pioneered the field of dwarf galaxies, discovered three new companions of Andromeda and invented the standard luminosity classification scheme for spiral and irregular galaxies. His studies have made him an authority on extragalactic distances.