His lifelong work was the study of the Milky Way, much of it in collaboration with his wife, Priscilla Bok, née Fairfield (1896–1975). In particular he investigated its structure, its distribution of stars, interstellar matter, and star-forming regions. In the 1930s he discovered the objects now called Bok globules and demonstrated that stellar associations are made up of young stars. In the early 1950s, with J. H. Oort and others, he pioneered the mapping of the Galaxy at radio wavelengths.