The Chicago Manual of Style

The Chicago Manual of Style (CMS) is a highly regarded style guide for American English, dealing with questions of style, manuscript preparation, and, to a lesser degree, usage. (Note that in the publications world, style means punctuation, italicizing, bolding, capitalization, tables, and so forth; not prose style.) Indeed, because of its sharp analyses of extremely intricate matters of punctuation and usage, it is used by publishing houses all over the English-speaking world, and is increasingly regarded as authoritative for the English publishing community in general.

The CMS is commonly used by publishers and editors as a last resort for questions of proper presentation of text.

It is published by the University of Chicago Press. The first edition was published by the University in 1906, under the title A Manual of Style. As of 2005, it is in its 15th edition. The CMS is currently published in hardcover, with a digital edition planned for release in 2006, however it still is pending (link). The CMS web site features a question-and-answer column and a full manual text search (members only).