Bart Jan Bok (April 28, 1906 – August 5, 1983) was a Dutch-American astronomer.
He was born in the Netherlands, but worked at Harvard University from 1929–1957. He then worked as director of Mount Stromlo Observatory in Australia for nine years, before returning to the United States as director of Steward Observatory.
He won the Bruce Medal in 1977, and was awarded the Henry Norris Russell Lectureship in 1982, and the Klumpke-Roberts Award in that same year.
A crater on the Moon is named after him, as is the asteroid 1983 Bok.