The Opposite of December... A Season of Separation is the debut full-length album by American metalcore band Poison the Well. It was released on December 14, 1999. Influential in the early popularization of metalcore around the turn of the 21st century, the album was the band's first on Trustkill Records and is now recognized as a landmark album in the genre due to its quality and influence. The album was the band's first release to appear on CMJ's charts, reaching number nine on the Loud Rock chart in May 2000. It had sold 30,000 copies by 2002. The release received numerous reissues on various formats over the years through such record labels as Good Life Recordings, Roadrunner Records, Shock Records and Rise Records and was digitally remastered in 2012.

In promotion of the album, Poison the Well toured the United States several times between December 1999 and September 2001 and also performed a handful of shows in Canada and Belgium. The bands that accompanied Poison the Well on these tours include Stretch Arm Strong, Twelve Tribes, This Day Forward, Brother's Keeper, NORA, Martyr A.D., Candiria, Origin, Cryptopsy, Codeseven, Love Lost but Not Forgotten, Cataract, Curl Up and Die, Eighteen Visions, Unearth, God Forbid and From Autumn to Ashes. Poison the Well also performed at notable festivals like CMJ MusicFest Marathon, in Manhattan, New York, Hellfest in Syracuse, New York (in both 2000 and 2001), Krazy Fest in Louisville, Kentucky, Gainesvillefest in Gainesville, Florida, Monster Fest in Burlington, Vermont, Mixed Messages in Minneapolis, Minnesota, Board Festival in Boston, Massachusetts, Fantasy Festival in Miami, Florida, and Good Life Summer Festival in Waregem, Belgium.

The Opposite of December... A Season of Separation's recording session and following promotional tours featured a great deal of member changes for Poison the Well. The album was recorded with vocalist Jeffrey Moreira, bassist Alan Landsman, drummer Christopher Hornbrook and guitarists Ryan Primack and Derek Miller. Former vocalists Duane Hosein and Aryeh Lehrer were both invited to provide backing vocals on a song. Primack quit immediately after the recording was completed and was briefly replaced by José Martinez. During the ensuing tours, Landsman was replaced by a slew of bassists including Michael Gordillo, Javier Van Huss, Albert and finally Iano Dovi, the last of which remained with the band to record their follow-up Tear from the Red. Miller was unable to consistently tour due to school obligations and was periodically substituted by Michael Peters and Matthew Tackett. Moreira also suffered a pneumothorax on the final promotional tour, leading Francis Mark to sing at several shows.