In Order:

• 1999: Episode I: The Phantom Menace
• 2002: Episode II: Attack Of The Clones
• 2005: Episode III: Revenge Of The Sith
• 1977: Episode IV: A New Hope
• 1980: Episode V: The Empire Strikes Back
• 1983: Episode VI: Return Of The Jedi

The Original Trilogy:

1977: Episode IV: A New Hope
1980: Episode V: The Empire Strikes Back
1983: Episode VI: Return Of The Jedi

The Prequel Trilogy:

1999: Episode I: The Phantom Menace
2002: Episode II: Attack Of The Clones
2005: Episode III: Revenge Of The Sith

Unrelated:

2008: Star Wars The Clone Wars (Animated Film)

- Episode I and II tell the stories about the Clone Wars that could not be included in the actual movie due to time conflicts with the release date and the time needed to cast, screen and film them.