The Idiran-Culture War is a fictional conflict in the midst of which Iain M. Banks' science fiction novel Consider Phlebas is set. His later book, Look to Windward, contains many references to the war: particularly the induced supernovae of two stars, which resulted in the death of billions of sentient creatures. Vague references to the war can also be found in Excession.

According to Banks' appendices to Consider Phlebas, the war began in 1327 AD, and continued for 48 years and one month. Total casualties amounted to 851.4 billion sentient creatures, including medjel (slaves of the Idirans), sentient machines and non-combatants. The war resulted in the destruction of over 91 million starships, fourteen thousand Orbitals and six stars.

The conflict was one of principles; the Culture went to war because the Idirans' fanatical imperial expansion, on religious grounds, threatened the Culture's very right to exist. Ultimately, the conflict would appear inevitable; the Idirans would not halt their expansion, because their Faith wouldn't allow it; the Culture is so ill-defined, having no borders or laws, that it may also have grown ceaselessly — as Horza , the protagonist in Consider Phlebas, observed. The two cultures would have been unlikely to forge a peaceful co-existence.

Despite the relatively small scale — in comparison with the rumoured conflicts of the past — the Idiran-Culture war is considered a significant event in (Banks') galactic history.