Some encyclopaedias require a brief biography of the contributor (e.g. 300 words) and contact details such as email address, the URL of a relevant website you might have. Writing a personal biography is an art in itself, but as a rule it should be concise and focused on the details relevant to the entry, publication and readership. For those wishing to write regularly in the academic world (and make applications for grants, scholarships, project funding, book/article proposals), it is worth having a well-crafted, stock, biography in your store cupboard which can be used each time, perhaps adjusting it slightly for different audiences. Some encyclopaedias may request a personal photo for use on the contributors section as well.
Originality
The work must be original, and it is worth consulting other encyclopaedias to check what has been written on your subject before; even Wikipedia. Usual considerations of plagiarism and copyright protection apply, but properly quoted and cited extracts would normally fall under the “fair use” principle widely recognised in scholarly and academic writing.
Sources / further reading
Encyclopaedias differ in the quantity of sources which they require/permit to be cited but this is normally a low number (e.g. 3). These sources should be ones where the ‘best’ information in your entry comes from, and the ‘best’ additional information for readers will be found. They are not ‘footnotes’ in the formal sense of the word, although large encyclopaedias with long entries such as Stanford do permit footnotes.
Academic encyclopaedias normally require that only ‘refereed’ publications may be cited, and most discourage citing of unpublished and inaccessible materials.
The editors will normally format the bibliographic details as they see fit during the copy-editing process, but they may provide detailed requirements in the guidelines. In the absence of specific advice, err on the side of caution and provide full details of the works you cite (Author, title, place and date of publication).
Likewise, encyclopaedias differ on the acceptability of citing Internet sources, and while this is increasingly common, they might differ on what type of internet source is acceptable (e.g. “.edu”, “.gov.” and “.org” domains may be considered more acceptable than “.com”). They discourage citing on-line versions of major printed texts (e.g. Encyclopaedia Britannica), preferring the original printed version, but when doing so, most require that the URL is included.
Some encyclopaedias prohibit or discourage the citing of the author’s own published work, except where that work is the only, or most, authoritative source available (e.g. Stanford).
Related entries
Some encyclopaedias end their entries with a ‘Related Entries’ section. This will normally be a list of key concepts or people mentioned in your entry for which there is a separate, dedicated entry in the encyclopaedia. If these are not known in advance, there is no harm suggesting some in your submission, you may be asked to contribute more!
Good luck and have fun…