Blocking is a theatre term that refers to the precise movement and positioning of actors on a stage in order to facilitate the performance of a play, ballet, film or opera. The term derives from the practice of 19th-century theatre directors such as Sir W. S. Gilbert who worked out the staging of a scene on a miniature stage using blocks to represent each of the actors (Gilbert's practice is depicted in Mike Leigh's 1999 film Topsy-Turvy).
In contemporary theatre, the director usually determines blocking during rehearsal, telling actors where they should move for the proper dramatic effect, ensure sight lines for the audience and work with the lighting design of the scene.
Each scene in a play is usually "blocked" as a unit, after which the director will move on to the next scene. The positioning of actors on stage in one scene will usually affect the possibilities for subsequent positioning unless the stage is cleared between scenes. Once all the blocking is completed a play is said to be "fully blocked" and then the process of "polishing" or refinement begins. During the blocking rehearsal usually the assistant director or the stage manager (or both) take notes about where actors are positioned and their movement patterns on stage.
It is especially important for the stage manager to note the actors' positions, as a director is not usually present for each performance of a play and it becomes the stage manager's job to ensure that actors follow the assigned blocking from night to night.
By extension, the term is sometimes used in the context of cinema to speak of the arrangement of actors in the frame. In this context, there is also a need to consider the movement of the camera as part of the blocking process (see Cinematography).
Stage directions 
|Look up stage right, stage left, upstage, or downstage in Wiktionary, the free dictionary.|
The stage itself has been given named areas to facilitate blocking.
- The rear of the stage is considered up-stage. This derives from the raked stage, where the stage sloped up away from the audience.
- The front of the stage is down-stage.
- Stage left and right, at least in British and North American theatre, refer to the actor's left and right facing the audience. Because this is sometimes misunderstood, the terms prompt (actor's or stage left) and bastard/opposite prompt (actor's or stage right) are also used. (See also Prompt corner)
- House left and house right refer to how the audience perceives the stage. The audience’s left is referred to as house left, and the audience’s right is referred to as house right. (These may also be called camera left and camera right for a filmed or sometimes unfilmed production or play.)
- Novak, Elaine Adams; Novak, Deborah (1996). Staging Musical Theatre. Cincinnati, Ohio: Betterway Books. ISBN 978-1-55870-407-7. OCLC 34651521.
- Spolin, Viola (1985). Theater Games for Rehearsal: A Director's Handbook. Evanston, Ill: Northwestern University Press. ISBN 978-0-8101-4002-8. OCLC 222012533.
- Cameron, Ron (1999). Acting Skills for Life. Toronto: Dundurn Press. ISBN 978-0-88924-289-0. OCLC 43282895.
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