The collection consists of research files and notes related to the study of supernovae, RR Lyrae stars, star populations, galaxies (including the Andromeda Galaxy), and various novae by German-born astronomer Wilhelm Heinrich Walter Baade (1893-1960), who joined the staff of the Mount Wilson Observatory in 1931. This collection forms part of the Mount Wilson Papers of the Observatories of the Carnegie Institution of Washington.

Wilhelm Heinrich Walter Baade (he did not often use his first two names) was one of the most important astronomers of the twentieth century. As an observer at the Mount Wilson Observatory, he ranks alongside Edwin Hubble in significance. Baade, however, was an excellent theoretician as well as observer. His interest in the stellar content of various star systems led him to develop his famous concept of stellar populations. And his observing skill led to his unexpected resolution of the inner parts of the Andromeda galaxy into individual stars. His work with the new 200-inch Hale telescope would eventually lead to a change in contemporary knowledge of the distances of the galaxies. Though his scientific method resulted in much of his work being published posthumously, Baade's impact on the development of astronomy was enormous.

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