According to his biographer, John Russell Taylor, Alfred Hitchcock got the idea for North by Northwest after driving north from LA to a house in Scots Valley.  To him, the bland plains of Bakersfield offered up one element of suspense: low-flying crop-dusting planes seemed sinister to him.  He asked himself, what if there were a faceless enemy attacking someone from one of those planes?  And so, the germ of the film was born many years before the actual shoot. 

Here are some more essential facts about the film:

-Although the United Nations didn't allow filming, Hitch sneaked a camera in there for for a short scene with Cary Grant.
-Originally, the director thought James Stewart would be the lead for the film.
-Unlike some of his other actors, he trusted Cary Grant's suggestions.  One day, it was clear to Grant that a Pullman car had been constructed in a slipshod manner.  Hitch immediately had the whole thing redone: without even looking at it.
-But Grant did cross the line once filming began. He said to others on the shoot that he didn't know if Hitch could pull of light comedy.  When this got back to Hitch, the director was royally annoyed.
--Cyd Charisse was originally suggested by MGM to be the heroine.  Instead, Hitchcock chose Eva Marie Saint, who had won the Oscar for On the Waterfront.  The only thing Hitchcock changed was the tone of her voice: he wanted her to lower it, and she was happy to do so.