Do you need your own style guide? That depends. Maybe an existing style guide meets all your needs or even has been adopted as your publications official style. In those cases, no, you dont need your own style guide.
Or maybe you repeatedly have to answer style questions that have no right or wrong answerfor example, Should commas be used before the conjunction in a series of words? Should traveling be spelled with one l or two? Should Congressional always be capitalized? Should state be capitalized in the phrase Washington state?* Typically a style guide will answer those questions, but maybe your boss (or one of your bosses, if you are blessed with more than one) doesnt like some of the answers. Or maybe you dont like some of the answers. Maybe you have recurring style questions that arent addressed in your favorite style guide, or maybe some aspects of the guide arent compatible with your publication. Returning to the example of Washington state (or Washington State, if you prefer), following a style guide (such as the Government Printing Office manual) that uses the two-letter postal abbreviations for states will cause trouble if a publication has abbreviated references to both Washington state and Western Australia (I encountered this conflict myself).
If you dont find a satisfactory existing style guide, do you need to create your own? Maybe, but you dont have to write the whole thing. Usually its easiest to pick an existing style and then define exceptions rather than try to define everything yourself. You also dont have to list all the exceptions at once; you can add them as you come across them.
If you havent chosen a style guide for the basis of your own house style, which one is right for you?
The Chicago Manual of Style is designed for university presses. For scholarly work, it is the standard. However, I consider it needlessly complicated, with about 160 pages of instructions for citing sources. Its so thick that your writers and editors may not have time to study and follow it. In fact, Why Would Anyone Use the Chicago Manual of Style? asked the Grammar Girl, Mignon Fogarty. Her answer: Because it has so much information that I cant find anywhere else.
The Associated Press guide is much simpler, and you might not need a lot of exceptions. It has a lot of rules, but it also has a lot of explanations. Its designed not just for editors but to help writers produce work that is accurate and clear.
The U.S. Government Printing Office Style Manual (free online) has lots of useful information, but it is more about typesetting than about content.
The Yahoo! Style Guide is especially useful when youre editing for publication on the Web.
The Modern Language Association of America style for documentation is widely used in the humanities, especially in writing on language and literature according to the association. The MLA publishes two authoritative explanations of MLA style: the MLA Handbook for Writers of Research Papers and the MLA Style Manual and Guide to Scholarly Publishing.
Countless other style guides exist. You may find these brief articles helpful in choosing the best style guide for you:
Richard Nordquist, Choosing a Style Manual and Documentation Guide
Mignon Fogarty, the Grammar Girl: Why Would Anyone Use the Chicago Manual of Style?
Richard Nordquist, Top 10 Free Online Style-Guides in English
* Quoted from the book The Editors Companion.
I had so many bosses (over the years) that I said I would create a wax museum of them. I told a co-worker about this and then asked one of my former bosses to sit very still. But when I showed the co-worker this purported first exhibit in my wax museum, the boss started talking. Later I complained to him, Now that guy thinks youre an animatronic robot!