The Berne Convention, the United Nations Declaration of Human Rights, and national law in many countries accord creators a moral right to be acknowledged as the author of their creative work. The use to which credits are put varies considerably from country to country and may have significant financial implications in those countries where the distribution of certain payments, such as residuals and royalties, is dependent on the credit accorded to the writer
The process by which credit is determined also varies; it may be the exclusive responsibility of the writer's guild or union: a collectively bargained agreement between producers and writers' unions or guilds; a matter of law; or of individually negotiated contracts. Credit disputes may be arbitrated by a guild or union or, in the absence of such processes, resolution may fall within the purview of common or contract law in the relevant country. Whatever the case may be, it is the responsibility of all writers to see to it that their work and the contribution of others is credited as accurately as possible and with a minimum of variation; the overall result of which is the recognition of the importance of the writer's contribution to the screen.
Below is a brief overview of the intention and rules regarding the most common credits given to writers. For a more comprehensive list and comparison of all IAWG member guild credit provisions, a pdf booklet is available for download here. These lists are for information purposes only, so if you have a dispute with regards to your writing credit, you should contact your guild, union or legal representative, as appropriate.
The term "story" means an original idea written for the screen which is distinct from a screenplay and consisting of the basic narrative, idea, theme or outline indicating character development and action. A "Story by" credit is appropriate when the screenplay is based on a story, as defined above, and not based on any pre-existing material.
Credit for story authorship in the form "Screen Story by" is appropriate when a story, as defined above, is based on source material though substantially new or different from the source material.
A screenplay consists of individual scenes and full dialogue, together with such prior treatment, basic adaptation, continuity, scenario and dialogue as shall be used in, and substantially contributes to, the final script.
A "Screenplay by" credit is appropriate when the screenplay is based upon a story or a screen story as defined above.
The term "Written by" is used when the writer(s) is entitled to both the "Story by" credit and the "Screenplay by" credit.
This credit shall not be granted where there is source material of a story nature. However, biographical, newspaper and other factual sources may not necessarily deprive the writer of such credit.
A "Narration Written by" credit is appropriate where the major writing contribution to a motion picture is in the form of narration. The term "narration" means material (typically off-camera) to explain or relate sequence or action (excluding promos or trailers).
"Based on Characters Created by" is a writing credit given to the writer(s) entitled to separated rights in a theatrical or television motion picture. This credit is accorded when a sequel to a theatrical or television motion picture is produced for television (excluding a television series).
When credit is accorded to a team of writers, an ampersand (&) shall be used between the writers' names in the credit to denote a writing team. Use of the word "and" between writers' names in a credit indicates that the writers did their work separately, one usually rewriting the other. This distinction is well established in the industry through custom and practice.
The possessory credit "a film by" or its variations, is accorded to a director who has written and directed the film; who has a significant body of work and whose reputation as a film-maker is such that it can make a significant contribution to the marketing of the film. Writers' guilds do not believe that the possessory credit should be used in any other circumstances.