Alfred Hitchcock's very free 1935 adaptation of John Buchan's novel was almost certainly the calling card that got him invited to make films in America. As a work of pure entertainment, it out-Hollywoods Hollywood. The plot is that of a thriller. But the tone is more reminiscent of Frank Capra's “It Happened One Night” (which won the previous year's Best Picture Oscar): a series of mostly comic episodes, about a couple, who are on the run by necessity, bristling with hostility, and absolutely destined to fall in love by the end.
There have been three official remakes; I've seen two, and they hold no interest at all. But the film's basic tone and structure have been so influential that it's fair to say there are scores of unofficial versions. Not least of these is “North by Northwest”; Hitchcock never denied that “The 39 Steps” was the template for that later masterpiece.