There’s a scene in the movie “Green Book,” when Don Shirley, a Jamaican American classically trained pianist, and his white chauffeur, Frank “Tony Lip” Vallelonga, climb into a blue Cadillac before setting out on a 1962 concert tour that would take them through a still-segregated United States, including potentially treacherous stops in the Midwest and the Deep South.

Shirley (played by Mahershala Ali) slides in the back seat. Vallelonga (Viggo Mortensen) takes the driver’s seat, prepared to leave New York for an eight-week tour. But before they hit the road, a manager slips Vallelonga a “Green Book,” explaining quickly that black people can’t stay everywhere and that the guide might help the chauffeur find accommodations for Shirley.

The chauffeur glances at the cover of the Green Book and tosses it on the passenger’s seat.

Despite the movie’s title, there are not many more references in the movie to the guide that was essential for black travelers in the 1930s, 1940s, 1950s and 1960s, when segregation was in full force in the United States.