Tomorrow, When the War Began is a 2010 Australian action-adventure war drama film written and directed by Stuart Beattie and based on the 1993 novel of the same name (the first in a heptalogy) by John Marsden. The film was produced by Andrew Mason and Michael Boughen. The story follows Ellie Linton, one of seven teenagers waging a guerrilla war against an invading foreign power in their fictional hometown of Wirrawee. The film stars Caitlin Stasey as Ellie Linton and features an ensemble cast including Rachel Hurd-Wood, Lincoln Lewis and Phoebe Tonkin. Production began in September 2009.

Principal photography began on 28 September 2009, and concluded on 6 November 2009; filming took place in the Hunter Region and the Blue Mountains, in New South Wales. The teaser trailer for the film was released on 31 March 2010. The film was released in Australia and New Zealand on 2 September 2010. It was later released on 15 April 2011 in the United Kingdom, and on 24 February 2012 in the United States.