Manual of Style
The Chicago Manual of Style started in 1891 in the University of Chicago Press. It was developed by the staff to aid writers and themselves. The Manual was composed of the rules in force at the press.
The Chicago Manual of Style is used in literature, history, the arts, the physical and natural sciences and social sciences. It is used by designers, editors and publishers.
If you are a member of any of the professions listed above or a student in one of them, you will need to use the Chicago Manual of Style in your papers. One of the best online tools for the Chicago Manual of Style is at the Purdue Online Writing Lab. It can be found at: https://owl.english.purdue.edu/owl/section/2/12/
For citations, the Chicago Manual of Style allows two systems: notes and bibliography and author-date. Which style you use depends on your profession and the journal or class you are writing for. This site has two tabs – one for notes and bibliography and the other for author-date: http://www.chicagomanualofstyle.org/tools_citationguide.html