Your instructor may assign a specific style for you to follow. If so, use the style consistently throughout your paper: in the layout of the paper (margins, line spacing, cover page), in the footnotes/in-text citations and in your final list of references.
ACS is the standard style used for Chemistry.
American Psychological Association (APA) style is the standard style used for psychology and many other academic disciplines, especially the social sciences.
APA Style Guides Online
APA Style Guide In Print
The Chicago Manual of Style provides two distinct citation styles: Humanities style (notes and bibliography) and Scientific/Social Sciences styles (parenthetical author/date references and reference list). Be sure to check with your instructor regarding which style they prefer that you use. Chicago style is sometimes called Turabian style, which is a modified version.
Chicago/Turabian Style Guides Online
Chicago/Turabian Style Guides in Print
Harvard is a parenthetical style used most commonly in the UK and Australia. Unlike other citation styles, there is no authoritative guide for Harvard style, so you may see small differences between guides. When using Harvard style, the most important thing is to consistently apply one guide. Here are some guides you may wish to choose from:
IEEE Style uses a notational method of referencing
Used primarily in Law
Modern Languages Association (MLA) style is one of several styles for academic citation. It is used in the humanities, especially English.
MLA Style Guides Online
MLA Style Guide in Print
Commonly used in medical and scientific journals