Many filmmakers regard editing as the single most important creative step in determining the look and shape of the finished film. A good editorlcan save a film that has been directed in a mediocre fashion, and poor editing can damage the work of even the finest director.

Editing is the work of joining shots (scenes recorded by the camera, usually on film) to assemble the finished film. The editor selects the best shots from the large amount of film footage (raw, unedited film) provided by the director and the cinematographer, assembles these in order, and connects them using a variety of optical transitions. In theory, the process of editing begins with the completion of filming, or cinematography. In practice, however, the editor may begin consultations with the producer and director and may even begin cuting the film, taking scenes and putting them together, while principal filming is being completed. Most editors, however, will not watch the process of filming or view the locations where the film is shot. This allows them to view the footage unhampered by knowledge about the actual conditions that existed in front of the camera and to visualize with greater freedom various ways of combining the shots.

Over the years, the basics of editing have remained relatively constant. The first task is to assemble a first version or rough cut, which is done by climinating all of the unusable footage containing technical or performance errors. These may include out-of-focus shots or shots containing unstable camera movement, lines where an actor has made mistakes in delivery, inaudible sound recordings, or lighting problems. Once all of this footage has been removed, the editor then assembles the remaining footage in a narrative sequence. This rough assembly will be pruned, refined, and polished to yicld the final cut. The final cut is the completed product of an editor's work. It includes the complete assembly and timings of all shots in the film's finished form. It is in going from the rough cut to the final cut that the real art and magic in editing lines.

With the introduction of computers, editors began to use a nonlinear, computer-based editing system. Film footage was converted to videotape, which was then digitized and stored on computer disk, giving an editor instantaneous access to any frame or single image, shot, or edited sequence distributed anywhere in the existing footage. The editor would then decide which footage to work on by using notes that described the characteristics, strengths, and flaws of particular shots. Prior to the 1990s. when the film industry adopted digital editing systems. editors worked directly with the actual film itself and had to search manually through all of the footage to find a desired shot or segment. This older approach was a linear system: the editor could only search for one shot at a time and had to do so by viewing footage sequentially, from beginning to end.

Digital systems made editing a much faster process, and the complex control they gave editors over the digitized footage helps explain why so many films had many more cuts and shot transitions than in cartier decades. Many shots were only a few frames long, less than a second of screen time.

White digital systems gave editors greater control over their footage and increased their ability to manipulate it in ever more elaborate Ways, these systems had disadvantages. Unlike editors who worked in linear systems, those using digital systems did not view a film image bur rather an electronic image on a small monitor screen, which was degraded in quality, with poor resolution. This could bias editors toward closc-ups because they would look better on the monitor than long shots. Furthermore, because the monitor's image was a poor guide to the visual qualities of the actual film images, editors were forced to rely more heavily on their notes about the footage. It has been argued that editors using linear systems got to know their footage better because they had to manually search through all of it to find what they needed. The editor working on a digital system would not access footage that the notes had excluded. With recent advances in digital technology, even these disadvantages have been addressed.