What is an Annotated Bibliography?
An annotated bibliography is a list of citations to books, articles, websites and documents where each citation is followed by a brief descriptive and evaluative paragraph (100 - 125 words); the annotation. The purpose of the annotation is to inform the reader of the relevance, accuracy, and quality of the sources cited.

The Process
After you have cited the book, article, or document using the MLA formatting style, you will write a short annotation that summarizes the central theme and scope of the book or article. Each annotation should include one or more sentences that (a) evaluate the authority or background of the author, (b) comment on the intended audience, (c) compare or contrast this work with another you have cited, or (d) explain how this work adds to your understanding of the topic.

Criteria
A good annotated bibliography has a summary of the source (what topics are covered? How is the information organized, presented?), an assessment of the source (is the source relevant to your research? What are the credentials of the author or organization? Is it reliable information, biased or objective?), and a reflection of the source (how does it fit into your research? Was the source helpful? Does it change your perspective of the topic).

Below are examples of both well-written and poorly written annotated bibliographies:

Sample of a well-written annotation:

"Calcutta: pollution and health." CBS News Special. By Ehrenreich, Bruce. 6 Feb. 2009. Television.

Ehrinreich is the author of a CBS News story about the devastating pollution in Calcutta, India. The story was developed from research carried out by a team of qualified academics from the School of Environmental Studies at the Jadavpur University in India. Ehrinreich’s research team conducted its studies between 2003 and 2005. The content covers air pollution, specifically the content of heavy metals in the air, and sound pollution. The information is supported with numerous graphs. Ehrinreich holds a PhD in Environmental science and Biology, as well as a master’s degree in Microbiology. The program was helpful in my research as it provided a great deal of relevant information and was presented in an interesting visual format.

Sample of a poorly written annotation:
"Calcutta: pollution and health." CBS News Special. By Ehrenreich, Bruce. 6 Feb. 2009. Television.

This was a good site about air pollution in Calcutta, because it had a lot of good information for my topic. I liked this site. It has more specific information than books and is not too much to read. It is authoritative because it is up to date and all rights are reserved.

(Information and examples taken from websites of Cornel University, Research & Documentation Online, and Ms. Dixon's Wiki)