Sometimes, two or more films in a series are shot and produced "back-to-back", which means simultaneously or within a short space of time. This is usually done to eliminate the need to rebuild sets and re-hire actors for sequels, and maintain audience interest in the film series. Films produced this way usually have a well-planned pipeline, where the first film may be in post-production as the second is being shot.
While sometimes a trilogy such as The Lord of the Rings is shot with all three parts back-to-back, it is much more common for only two parts to be shot this way. Often, in a trilogy, the first film will be made on its own, and if it is a success, the remaining two parts will be produced back-to-back. This approach was pioneered by the second and third parts of the Sleepaway Camp trilogy, and has since been applied to the Back to the Future trilogy and The Matrix trilogy. Back to the Future Part II, and later, The Matrix Reloaded both ended with the words "To be concluded," a variant on the traditional "To be continued," and a trailer for their respective upcoming sequels.
The following is a list of films that have been produced this way:
Les Misérables (1934)
The Tiger of Eschnapur (1938) and The Indian Tomb (1938)
The Count of Monte Cristo (1943)
Stars Over Colombo (1953) and The Prisoner of the Maharaja (1954)
The Count of Monte Cristo (1954)
And Quiet Flows the Don (1958)
The Tiger of Eschnapur (1959) and The Indian Tomb (1959)
Mistress of the World (1960)
The Three Musketeers (1961)
The Count of Monte Cristo (1961)
Kali Yug: Goddess of Vengeance (1963) and The Mystery of the Indian Temple (1964)
Anatomy of a Marriage: My Days with Françoise (1964) and Anatomy of a Marriage: My Days with Jean-Marc (1964)
Der Schatz der Azteken (1965) and Die Pyramide des Sonnengottes (1965)
War and Peace (1966 and 1967)
Die Nibelungen (1966 and 1967)
Kampf um Rom (1968 and 1969)
The Emigrants (1971) and The New Land (1972)
The Three Musketeers (1973) and The Four Musketeers (1974), shot as one film but split into two during post-production
Superman (1978) and Superman II (1980) (see also Superman II: The Richard Donner Cut, released 2006)
Trail of the Pink Panther (1982) and Curse of the Pink Panther (1983), parts of the Pink Panther series
Missing in Action (1984) and Missing in Action 2: The Beginning (1985)
King Solomon's Mines (1985) and Allan Quatermain and the Lost City of Gold (1986)
Jean de Florette (1986) and Manon des Sources (1986)
Sleepaway Camp II: Unhappy Campers (1988) and III: Teenage Wasteland (1989), sequels to the 1983 film Sleepaway Camp
The Toxic Avenger Part II (1989) and The Toxic Avenger Part III: The Last Temptation of Toxie (1989) were filmed as one movie but was later re-edited into two
La Révolution française (1989)
Back to the Future Part II (1989) and Part III (1990), of the Back to the Future film series
Child's Play 2 (1990) and 3 (1991), parts of the Child's Play horror saga.
Critters 3 (1991) and 4 (1991), the last two films of the Critters series
Smoking/No Smoking (1993)
The Three Colours Trilogy: Blue (1993), White (1994) and Red (1994)
Joan the Maiden (1994)
Blue in the Face (1995) was conceived and filmed completely ad libbed immediately following production of Smoke (1995)
Bullet to Beijing (1995) and Midnight in Saint Petersburg (1996)
Wishmaster 3: Beyond the Gates of Hell (2001) and Wishmaster: The Prophecy Fulfilled (2002)
The Lord of the Rings: The Fellowship of the Ring (2001), The Two Towers (2002) and The Return of the King (2003)
The Matrix Reloaded (2003) and The Matrix Revolutions (2003), parts of the Matrix series
Kill Bill: Volume 1 (2003) and Volume 2 (2004), which were originally shot as one film and later edited into two
Anchorman: The Legend of Ron Burgundy and Wake Up, Ron Burgundy: The Lost Movie (2004), the second being a direct-to-video effort assembled from deleted scenes and outtakes of the first
Ginger Snaps 2: Unleashed (2004) and Ginger Snaps Back: The Beginning (2004)
Return of the Living Dead: Necropolis (2005) and Rave to the Grave (2005), the fourth and fifth films in the Return of the Living Dead series
Pirates of the Caribbean: Dead Man's Chest (2006) and At World's End (2007), the second and third films in the Pirates of the Caribbean series
Flags of Our Fathers (2006) and Letters From Iwo Jima (2006)
Arn – The Knight Templar (2007) and Arn – The Kingdom at Road's End (2008)
Che Part 1: The Argentine (2008) and Che Part 2: Guerilla (2008)
Anaconda 3: Offspring (2008) and Anacondas: Trail of Blood (2009)
Pulse 2: Afterlife (2008) and Pulse 3: Invasion (2008)
The Girl Who Played with Fire and The Girl Who Kicked the Hornets' Nest were filmed back-to-back and released in 2009.
Arthur and the Revenge of Maltazard (2009) and Arthur 3: The War of the Two Worlds (2010), which were edited into Arthur and the Great Adventure (2010) for release in the United Kingdom
Harry Potter and the Deathly Hallows – Part 1 (2010) and Harry Potter and the Deathly Hallows – Part 2 (2011)
All the chapters in the Adams Apples film series were filmed back-to-back.
The Twilight Saga: Breaking Dawn – Part 1 (2011) and The Twilight Saga: Breaking Dawn – Part 2 (2012)
The Bollywood films Gangs of Wasseypur - Part 1 and Part 2 were originally shot as a single film measuring a total of 319 minutes, but since no Indian theatre would volunteer to screen a five-plus-hour movie, it was divided into two parts (160 mins and 159 mins, respectively) for the Indian market.
Nymphomaniac (2013) was originally supposed to be only one complete entry; but, because of its four-hour length, Lars von Trier made the decision to split the project into two separate films.
The Hobbit Motion Picture Trilogy films subtitled An Unexpected Journey (2012), The Desolation of Smaug (2013) and The Battle of Five Armies (2014)
The Hunger Games: Mockingjay – Part 1 (2014) and The Hunger Games: Mockingjay – Part 2 (2015)
The sequels to Fifty Shades of Grey, Fifty Shades Darker and Fifty Shades Freed, will be filmed back-to-back.
The four sequels to 2009's Avatar
Avengers: Infinity War and its untitled sequel, part of Phase 3 of the Marvel Cinematic Universe, will be released in two parts, in 2018 and 2019, respectively.
List of films produced back-to-back Wikipedia
Though not shot entirely back-to-back, the final scene of Star Wars: Episode III – Revenge of the Sith was shot in Tunisia during the production of Star Wars: Episode II – Attack of the Clones in order to avoid another trip to Tunisia for a single scene.