Judas O (also known as Judas Ø) is a collection of B-sides and rarities by The Smashing Pumpkins. Initially released as free downloadable tracks by the band, it was ultimately packaged as a bonus disc in a limited-edition printing of the greatest hits collection Rotten Apples. The songs are largely from the Mellon Collie and the Infinite Sadness, Adore, and Machina/The Machines of God recording sessions, and some tracks can be found on The Aeroplane Flies High, and Machina II/The Friends & Enemies of Modern Music. Judas Ø is considered to be the sister album to Pisces Iscariot, a collection of B-sides and rarities from the Gish and Siamese Dream era.

All tracks written by Billy Corgan, except for "Believe" written by James Iha and "Rock On" written by David Essex.