This site created by the esteemed Purdue Online Writing Lab (OWL) provides help a guide to APA, the most commonly used format to cite sources within the social sciences.
The Web-based edition is a fully searchable version of the Associated Press Stylebook, including an A-Z guide to usage, spelling, and a pronunciation guide with audio files.
This online site provides access to both the 15th and 16th edition. Both editions are completely searchable, offering ready access to the complete guidelines and examples. Also included are a Style Citation Quick Guide, fully searchable Q&A files, as well as sample forms, letters, and style sheets.
The MLA format is used by many disciplines in the humanities, most notably within the study of language and literature.