Lucasfilm has registered six different movie titles for Indiana Jones 4 with the MPAA according to /film. The proposed titles include:

Indiana Jones and the City of Gods

Indiana Jones and the Destroyer of Worlds

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Indiana Jones and the Fourth Corner of the Earth

Indiana Jones and the Kingdom of the Crystal Skull

Indiana Jones and the Lost City of Gold

Indiana Jones and the Quest for the Covenant

Movie Picture

According to the site, City of Gods has been long rumored to be the working title of the production.

Time will tell on which of the above titles (if any) will be used for the final release next May!