It is rumoured to be set after Goku's defeat of Kid Buu (the final bad guy in the Dragonball Z series) and before the World Martial Arts tournament which ended the DBZ series and was set 10 years after the fall of Buu.
This could mean a difficult transition for those not familiar with the Z world as it may require a lot of presumed backstory. 2009's "Dragonball Evolution" started at the beginning, going through Goku's training and his first meetings with Bulma and Yamcha. Then again, this setting for the new film also gives the director almost a clean slate: all baddies have been defeated and there are 10 undocumented years during which almost anything could have happened!
