Holy war may refer to:

• religious war, a war where one or more sides claim to have been led by or authorized by God.
• flame war, a long, intensive and heated discussion over a particularly controversial issue.
• Holy War (sports rivalry), the nickname of some traditional sports rivalry.
• "Holy War", a song by Manowar from their album Fighting The World.
• "Holy Wars", a song written by Megadeth in 1990 on their album Rust in Peace.
• Holy War, a Metagaming Concepts microgame designed by Lynn Willis.
• The Holy War, a In Nomine campaign run by one of the Steve Jackson Games editors, whose logs are posted online.