A footnote is a type of internal citation that directs readers to the source or sources of the information contained in the main part of the document. When footnotes are used, a subscript will appear immediately following the statement requiring a citation. At the bottom of the page the statement appears on, below a line separating the main text from the footnotes, the author will cite the source of the statement next to a number corresponding to the above-the-line subscript.
Endnotes are similar to footnotes, but when endnotes are used, the citations are found at the very end of the book or paper in a "Citations" section. Subscripts are still used and are in the same place as they would be with footnotes; however, rather than having citations at the bottom of each page, all of the citations are consolidated and placed in one location.
There are three basic situations in which footnotes should be used. The first is whenever an author is discussing an idea or making an assertion that is the product of another writer or institution. The second is when a statement of fact is made that should be supported by outside evidence. The third situation in which footnotes are appropriate is when additional clarification of a statement would be helpful, but would be awkward to place in the main text.
There are a variety of formats for citations contained within footnotes. Various professions, such as the legal profession, for example, may have their own specific rules for citations. Many branches of academia use consistent citations formats in research papers and other publications. Whatever the style, the basic information to be included is typically the title of the source, the author of the source, the date of publication and the page or pages on which the information can be found.