A citation style is merely a set of conventions established by a particular professional academic organization to make providing references simple and clear. The goal of any citation style is consistency, but each has its own idiosyncrasies that must learned. Three of the most popular, and their official style guides, are
While these official style guides are the only place to get the full details for every citation situation and for answers to specific questions about formatting in each style, all three have been summarized in a number of handbooks and websites. Unfortunately, not all summaries are accurate or up-to-date, so you will find inconsistencies on various websites, in various books, and even among your own instructors, who may well modify one of these styles for their own classroom use.
As noted, here at Adelphi, we have adopted Diana Hacker’s A Writer’s Reference, 5th edition, (Bedford/St Martin’s Press) as our default handbook. The handbook includes summaries of the three styles above. This means you can assume the guidelines for MLA, APA and Chicago outlined in A Writer’s Reference are acceptable in your class unless your instructor explicitly tells you otherwise. You may also use the online version at dianahacker.com/writersref. But if you are ever in doubt about what citation style to use, simply ask your instructor.