George Harrison wrote this. It was inspired by his wife, Pattie.
A little after half way through the song, John Lennon makes a reference to Elmore James, a Blues musician: "Elmore James got nothin' on this." If you listen to the song "Madison Blues" by Elmore James, the tune is very similar to "For You Blue." (thanks, Ben - Encinitas, CA)
John Lennon played the slide guitar part. The Beatles performed this in their last movie, Let It Be, and Lennon can be seen using a shotgun shell for the slide.
The version on Anthology 3 and also the Let It Be... Naked album are different takes from earlier in the January 25, 1969 session (1/25/69) when this was recorded. The Naked version is the same one seen in the Let It Be film. (thanks, Bertrand - Paris, France)
Harrison played this on his 1974 Dark Horse tour.
This hit #1 along with " The Long and Winding Road," which was its A-side. (thanks, Adrian - Wilmington, DE)
This was originally titled "George's Blues." (thanks, Bertrand - Paris, France)