Filming "back-to-back" is the practice of filming two or more movies as one production, reducing costs and time.
Trilogies are common in the film industry, particularly in science fiction, fantasy, action, horror, thriller, and adventure genres. Production companies may choose, if the first film is a financial success, to green-light a second and a third film at the same time and film them back-to-back. In a case where a lengthy novel is split into multiple installments for its film adaptation, those installments will usually be filmed back-to-back.
In modern filmmaking, the entire cast and crew for each film is assembled from scratch for each project, and each of them is laid off as soon as they complete their assigned tasks. Almost all participants in the industry are freelancers, who move easily from one project to the next and do not have much loyalty to any particular studio, as long as they get paid.
This differs from the old studio system in which studios carried large numbers of cast and crew on their payrolls under long-term contracts. To borrow a factory analogy, studios transitioned from using a single assembly line with an integrated staff to continuously churn out one film after another to building and disassembling separate assembly lines (each with its own unique staff) for every single film.
The advantage of the latter system is that film studios no longer have to bother either with paying people who are not involved in a current film production, or with green-lighting films very frequently so as to efficiently exploit sunk costs in their human resources. However, this also means that when they want a particular person for a film, that person may be unavailable because they are already committed to another film for another production company for that particular time slot. In turn, for every single film, studios (and ultimately their investors, shareholders, or backers) end up bearing massive transaction costs because they not only have to get the right person at the right price, but at the right time, and if they cannot get that person, they have to scramble to locate a satisfactory substitute. All successful directors and producers have certain favorite cast and crew members whom they prefer to work with, but that is of no help to the studio if that perfect character actor, costume designer, or music composer is already fully booked.
Therefore, if a film does well at the box office and appears to have established a winning formula with a particular cast, crew and storyline, one way to minimize these transaction costs on sequels is to reassemble as much of the team as soon as possible (before anyone dies, retires, or commits to other possible scheduling conflicts) and sign them to a single production that will be edited, released, and promoted as multiple films. This also minimizes the problem of stars visibly aging between sequels that do not have significant time gaps written in between them.
- Superman and Superman II were filmed simultaneously in 1977 to be a two-part epic. However, due to off-screen difficulties between the producers and director Richard Donner, production on the sequel was stopped in order to finish the first film for a December 1978 release. Filming on Superman II resumed in 1979 with a new director (Richard Lester), and was released in Australia in December 1980 and in the UK and US in 1981.
- After the success of the 1985 film Back to the Future, the two sequels Part II and Part III were in production from February 1989 until January 1990 with only a three-week break in principal photography between films and some of the filming of the third film overlapping with the second. The two films were released six months apart, in November 1989 and May 1990 respectively.
- The Lord of the Rings trilogy was filmed entirely over 438 days in New Zealand from October 1999 until December 2000 with pickup shots done prior to each film's theatrical release from 2001 to 2003. Likewise, The Hobbit trilogy was filmed back-to-back in New Zealand from March 2011 until July 2012.
- The Matrix Reloaded and The Matrix Revolutions were filmed back-to-back from March 2001 until August 2002, and released six months apart, in May 2003 and November 2003 respectively.
- Kill Bill: Volume 1 and Volume 2 were filmed as one film from June 2002 until March 2003, and later split into two "volumes" and released six months apart, in October 2003 and April 2004 respectively.
- Pirates of the Caribbean: Dead Man's Chest and Pirates of the Caribbean: At World's End were filmed back-to-back from February 2005 until January 2007, and released a year apart, in July 2006 and May 2007 respectively.
- Harry Potter and the Deathly Hallows - Part 1 and Part 2 were filmed back-to-back from February 2009 until June 2010, with reshoots for the second film concluding in December 2010. The two films were released eight months apart, in November 2010 and July 2011 respectively.
- The Twilight Saga: Breaking Dawn - Part 1 and Part 2 were filmed back-to-back from November 2010 until April 2011, with reshoots for the second film taking place in April 2012. The two films were released a year apart, in November 2011 and November 2012 respectively.
- Fifty Shades Darker and Fifty Shades Freed were filmed back-to-back from February 2016 until July 2016. The two films were released a year apart, in February 2017 and February 2018 respectively.
- Avengers: Infinity War and Avengers: Endgame were filmed back-to-back from January 2017 until January 2018, with reshoots for the second film concluding in October 2018, with the films released 12 months apart, in April 2018 and April 2019 respectively.
- The four as-yet-untitled sequels to Avatar are being filmed back-to-back in two two-film blocks.
- The two as-yet-untitled sequels to Mission: Impossible - Fallout will be shot back-to-back. The projects are scheduled for July 23, 2021 and August 5, 2022 release dates.