Chicago Manual of Style — Ref. Desk Z253.U69 2010 or online.
There are two versions of Chicago-style documentation, one which uses notes and one which uses in-text author-date citations. In history, it is conventional to use the "notes" style (either with footnotes at the bottom of the page or endnotes at the end of the document).
In some editions of the Chicago manual, this system is called "style A" or "documentation one." Historians do not generally use author-date citations ("style B" or "documentation two")