The following is a short guide to the three most common citation styles for essay writers (though different instructors may have their own requirements or local variants). CMS is used in the humanities and history by those who prefer the traditional look of footnotes or endnotes rather than in-text citations (though CMS also has a parenthetical citation style). MLA is the most common in-text citation style in the humanities; APA, in the social sciences. Listed are the formats for the in-text citation or note and for the bibliographic reference.
In-text citations direct the reader to an entry in a list of references. Such citations consist of two elements: a signal phrase and a parenthetical. One may choose to put the citation information in either element. Experienced writers often weave the author’s name into the signal phrase:

MLA: Schwartz characterizes Hamlet as “a war of masculine wills” (21). / This psychoanalytic perspective sees Hamlet as “a war of masculine wills” (Schwartz 27). Citing whole text: Schwartz surveys psychoanalytic readings of the play.

APA: Schwartz (1980) characterizes Hamlet as “a war of masculine wills” (p.27). / This psychoanalytic perspective sees Hamlet as “a war of masculine wills” (Schwartz. 1980. p. 27). Citing whole text: Schwartz (1980) surveys psychoanalytic readings of the play.

For more  information see  essay citations.