When citing sources that you find on the Internet you only need to include a retrieval date if the information you viewed is likely to change over time (p. 192). If you reference an article from Wikipedia, for example, you would want to include a retrieval date because information in a wiki can be subject to a lot of change.
General Format
In-Text Citation (Paraphrase):
(Title of specific document, Year)
NOTE: If the title of a document is long, use a shortened version for the
in-text citations.
In-Text Citation (Quotation):
(Title of specific document, Year, page or paragraph number [if available])
References:
Title of specific document.(Last update or copyright date; if not known, put n.d.).
In Title of website. Retrieved from URL of specific document
Example
In-Text Citation (Paraphrase):
(Indoor Air Quality, n.d.)
In-Text Citation (Quotation):
(Indoor Air Quality, n.d.)
References:
Indoor Air Quality and Allergies (n.d.). In Asthma and Allergy Foundation of America.
Retrieved May 8, 2010 from http://www.aafa.org/display.cfm?id=8&sub=16&cont=56