Depending on the way in which they record sources, scholarly reference styles can be divided into three main categories: documentary notes styles, parenthetical (or author-date) styles, and numbered styles. Within each category there are several, slightly different reference styles.
The different categories are described below. For information about specific reference styles, see
Documentary note styles
In documentary note styles (documentary-note citation systems), references are given in footnotes or endnotes. The notes are indicated by digits, which then recur with the full reference at the bottom of the page (footnote) or after the entire text (endnote). The digit is usually placed after the full stop ending the sentence to which the reference belongs.
Oxford and MHRA are documentary note reference styles.
Parenthetical styles or author-date styles
In parenthetical, or author-date styles, in-text references are given within parentheses before the full stop of the sentence containing the reference.
APA, Harvard, and MLA are parenthetical reference styles.
In numbered styles, sources are referred to with Arabic numbers within square brackets or in superscript, and the references are listed in a numbered reference list after the text. References are numbered in the order in which they first appear in the text.
Vancouver and IEEE are numbered styles.