39/Smooth is the debut studio album by American rock band Green Day, released on April 13, 1990, by Lookout Records. It was the band's only album to feature drummer John Kiffmeyer. Jesse Michaels of Operation Ivy contributed the artwork on the album. The inner sleeve shows handwritten lyrics by Billie Joe Armstrong and letters by drummer John Kiffmeyer and Lookout owner Larry Livermore to I.R.S. Records, rejecting a fake offer to sign to the label and declaring its loyalty to Lookout (however, the band would later leave the label and move to major label Reprise Records). There were no official singles released from the album, although "Going to Pasalacqua" was released as a mock-up single in a Green Day singles box set entitled Green Day: Ultimate Collectors.

39/Smooth was later re-released, along with the band's two previous extended plays 1,000 Hours and Slappy, and the song "I Want to Be Alone" (from The Big One, a compilation album released by Flipside Records in 1990) on the 1991 compilation 1,039/Smoothed Out Slappy Hours, which also used the same cover sleeve as 39/Smooth.