During the first year after publication, Author shall not Publish or authorize to be Published, without the written permission of the Publisher, any full-length work specifically intended to supplant the Work in the marketplace, and which would clearly and directly harm the sale of the Work. [If Author has written or, within [six months/one year] of publication of the Work, writes, a prequel or sequel based in whole or in part on the Work (with similar look, premise, feel, characters, style, and/or contents), Author shall first offer the prequel or sequel to Publisher, who shall have 30 days to respond in writing to Author's proposal. If Publisher notifies Author that it does wish to Publish the prequel or sequel, the parties shall negotiate in good faith for a period of 90 days with respect to the terms of such publication. If Author and Publisher do not reach an agreement on the material terms within such period, Author is free to Publish the prequel or sequel with another publisher or on his or her own.
Publishers' standard contracts often contain clauses restricting the author from publishing another book based on the material in the current work, or from publishing material competing with the sale of the current work. These clauses are one-sided as the publisher will not make the same commitment to you.
As an advocacy matter, the Authors Guild believes that authors must be free to write. Reasonable non-compete clauses are those that only prevent an author from selling the same or extremely similar material to another publisher for a limited time period, such as a year or two after publication. If you are an expert in a field, you should add a clause stating that any such limiting clause will not prevent you from writing another book on your chosen subject. Any non-compete clause should be simple: only the publisher can publish the current title, long excerpts from it, or a substantially similar work. Anything more is an unfair restriction on the author's livelihood.
A broadly worded non-compete clause can cause considerable harm. Depending on the scope of the clause, the publisher might claim that the characters in a novel or children's story may not be used in sequels and prequels, or that the author of a textbook may not write other works on the same subject, or that one cookbook or other specialized work is all that an author may write without the publisher's release from the non-compete clause. Though such claims might be held unenforceable in court because judges require that these terms be reasonable in scope and not unduly restrictive, it is obviously better to limit the publisher's ability to make such a claim in the first place.
The ways to appropriately limit a non-compete clause will vary, depending on the contract language and nature of the book. Generally, it can be achieved by (1) stating that the clause applies only to works that "directly injure the sale" of the book under contract, (2) limiting the non-competition to the specific text of the book under contract, and (3) limiting the non-competition in time so that it remains in effect for only a certain number of years (the fewer, the better) and that the author is free to write a new book on the same subject when it expires. The Model Contract contains an example of a non-compete clause that is acceptable in most circumstances. It also contains a reasonable, limited option for sequels and prequels that may be applicable for certain types of works of fiction.
Some trade publishers of fictional works will agree to delete a non-compete clause from their contracts. However, the same cannot be said for publishers of nonfiction works, which may be less willing to negotiate the terms of a non-compete clause, regardless of whether they are a trade, academic, or professional publisher.
If there is a project that you wish to take on that you are concerned could be perceived as competitive with the work covered by the contract, ask your publisher to specifically waive any objection to that project.