Job Roles - Editor

http://nofilmschool.com/2014/02/video-the-history-of-editing-eisenstein-the-soviet-montage-explained

Editors are one of the key Heads of Department on feature films, responsible for First Assistant Editors, and on bigger productions, Second Assistants and Trainees.

The Editor works closely with the Director, crafting the daily rushes into a coherent whole and a story. To ensure that the story flows effortlessly from beginning to end, each shot is carefully chosen and edited into a series of scenes, which are in turn assembled to create the finished film, giving the film a 'vision'.

Editors work long, unsociable hours, often under pressure, in an edit suite. They are employed on a freelance basis by the Producer (sometimes with the approval of the film's financiers), based on their reputation and experience. 

The Editor works closely with the Director before shooting begins, deciding how to maximise the potential of the screenplay. Editors check the technical standards, as well as the emerging sense of story, and the actors' performances.

Because scenes are shot and edited out of sequence, Editors may work on scenes from the end of the film before those at the beginning, and must therefore be able to maintain a good sense of how the story is unfolding.

Editors select the best takes and edit them together to create scenes. In some cases, an improvised line or an actor's interpretation of their role may create some on-screen magic that can be developed into a new and exciting scene.

http://creativeskillset.org/job_roles_and_stories/job_roles/2940_editor 
http://www.bectu.org.uk/