Although Wikipedia -- an online compilation of information anyone can submit to -- does not represent the kind of peer-reviewed source that most research papers should include, you may choose to refer to it in your paper. If so, American Psychological Association guidelines tell writers to follow the citation and references page format for an online reference work with no author or editor.
Citation and Reference Format
On your references page, the source information should begin with the entry name, followed by the date in parentheses, In Wikipedia and Retrieved from with the specific URL for the page, with a period between each concept but no punctuation at the end, as follows:
Thomas Jefferson. (n.d.) In Wikipedia. Retrieved from http://www.wiki.org/thomasjefferson
Indicate which ideas came from Wikipedia in your paper by adding a signal phrase or parenthetical citation that gives the entry word or words:
The founding fathers believed such a government was not sustainable ("Thomas Jefferson," n.d.).
Note the title of the entry should appear in quotation marks just as the title of an article with no author. A direct quote from an online, non-paginated source such as Wikipedia should also include a paragraph indication to help the reader find the quote: ("Thomas Jefferson," n.d., para. 3).