40 Greatest Hits is a two-record compilation that, true to the title, contains forty hit singles from country music icon Hank Williams. It was released in 1978 by Mercury Records — who under PolyGram became responsible for the MGM tape vault — on the 25th year anniversary of Williams' death. Significantly, it was the first anthology in quite some time that did not subject Williams' recordings to either rechanneled stereo, posthumous overdubs, artificial duets with family members (like his son Hank Jr.), or most or all of the above. Because of both this major fact, and the value-for-money attraction of having a deeper song selection than previous single-disc compilations issued previously by MGM Records, many reviewers consider this anthology to be the perfect starting point for newcomers to Williams' recorded legacy.

In 2003, the album was ranked number 129 on Rolling Stone magazine's list of the 500 greatest albums of all time.

Except where otherwise indicted, all tracks composed by Hank Williams.