In this article we adopt the framework of Just War doctrine to assess whether the 2003 invasion of Iraq was just. The six criteria against which we assess the justice of going to war are Just Cause, Right Authority, Right Intention, Reasonable Prospect of Success, Proportionate Cause and War as Last Resort. We focus upon what was known and said by the US, British and Australian governments around the time they decided to invade and consider whether there was sufficient justification and authorisation for the Iraq War. The key pre-war issues discussed include alleged Iraqi possession of WMD and links to terrorist organisations, and the meaning of UN Security Council resolutions. We conclude that, as the Just War criteria were not satisfied, the invasion of Iraq was unjust.