The past century has seen major advances in diffraction gratings, motivated by pressure for new and better data in two rather distinct fields: laboratory spectroscopy—aimed at understanding atomic structure and testing quantum theory—and astrophysical spectroscopy—aimed at understanding objects ranging from the Sun and stars to faint sources at the limit of detection. In this historical account I trace some of the hard‐won gains in the technology of the ruling machines that produce the gratings, and I touch on the role that larger and higher‐quality gratings have played in scientific advances. I focus on the work at the Mount Wilson Observatory, where I directed the diffraction‐grating laboratory from 1948 to 1963, but I do so with full recognition of the important contributions made at numerous other laboratories, especially those at The Johns Hopkins University, the Massachusetts Institute of Technology and the Bausch & Lomb Optical Company.