The Chicago Manual of Style , abbreviated as CMS is a style guide for American English published since 1906 by the University of Chicago Press. Its 15 editions have prescribed writing and citation styles widely used in publishing. The CMS deals with aspects of editorial practice, from American English grammar and usage to document preparation.The online edition includes the searchable text of the 15th edition with features such as tools for editors, a citation guide summary, and searchable access to Q&A, where University of Chicago Press editors answer readers' style questions

The Chicago Manual of Style online is a reference style tool available electronically. It allows two different type of reference styles:

The Author-Date System used in physical, and, natural sciences, and

Notes and Bibliography Style used in literature, history, social sciences,  and the arts.        

New Features in the Fifteenth Edition of The Chicago Manual of Style

Updated material throughout to reflect current style, technology, and professional practice

New coverage of journals and electronic publications

Comprehensive new chapter on American English grammar and usage by Bryan A. Garner (author of A Dictionary of Modern American Usage)

Updated and rewritten chapter on preparing mathematical copy

Reorganized and updated chapters on documentation, including guidance on citing electronic sources

Streamlined coverage of current design and production processes, with a glossary of key terms

New diagrams of the editing and production processes for both books and journals, keyed to chapter discussions

Descriptive headings on all numbered paragraphs for ease of reference.