"Cats" is based on the poetry of T.S. Eliot, specifically his late and rather whimsical work titled "Old Possum's Book of Practical Cats." It tells the story of the annual gathering of Jellicle cats during which one cat is selected to go to the Heaviside layer, a metaphorical paradise.
The composer of the musical, Andrew Lloyd Webber, recalls this poetry book by T.S. Eliot as being a particular childhood favorite. The songs of the musical are Eliot's verse set to music with the exception of the song "Memory." Eliot's wife, Valerie, attended a concert of these works and gave her blessing for Webber to adapt the songs into a musical.