Any time a writer uses information that the writer did not create her/himself (whether it's paraphrased or quoted, whether it's a chart, graph, picture, or drawing), that writer must cite the original source of the information. If you cite a source, you should also create a Works Cited entry.
If a writer doesn't cite his/her sources, s/he is PLAGIARIZING. Plagiarism usually will result in a zero for the paper, in addition to other penalties (in some cases, suspension or expulsion). Also, plagiarism is a civil crime - you can be sued by the original author.
The Modern Language Association (MLA) is a group that sets standards for writing in American English. They are one of several groups that has created rules for how borrowed information should be cited and referenced within writing. The MLA system is one that is used by most primary and secondary schools in the U.S. As new methods of communicating are introduced, MLA creates new rules for citing those new types of sources.
The Online Writing Lab (OWL) at Perdue website keeps a very up-to-date reference guide of the latest MLA rules.
There are a few basics to keep in mind when referencing any source; check out the slide show below for a quick overview.
Remember: Your sources need to be RELIABLE, which is why you shouldn't use Wikipedia!