A footnote assembles all information a reader would require if she wanted to look up the sources you consulted. In the case of a book, that information is the author's name as it appears on the title page, the title and subtitle of the book, the name of the publisher, the city in which the publisher's office is located and the year in which the book was released. The last piece of information included in a footnote is the page number. All footnotes are numbered. If you are writing a book, do not run your footnotes sequentially all the way through. Instead, with each new chapter, your first footnote will be "1."
Now, let's look at some sample footnote entries.
A book with a single author:
1. Stephen Frye, The Ode Less Travelled: Unlocking the Poet Within (New York: Gotham Books, 2006), 159.
Please note that commas, not periods, separate the different elements of the citation. Also, there is no "page," "pg" or "p" before the paper number.
If you cite the same book again, use a simplified footnote:
2. Frye, 17.
A magazine or journal article:
3. Fainche Ryan, "Team of Equals," Reality (March 2009): 31.
The date---month and year in this case---is the major difference between the footnote for a book and that for a magazine.
Material from a website:
4. Roger Crowley, "The Guns of Constantinople," HistoryNet.com, http://www.historynet.com/the-guns-of-constantinople.htm (accessed August 3, 2009)
So much useful information is available online. That said, websites have a way of editing or replacing their information, and sometimes websites just vanish. Therefore, it is essential to cite when you consulted your online source.
The footnote is both the writer and the reader's friend. It identifies the writer's sources, and indicates to the reader where to find more information on a particular subject.