An annotated bibliography lists citations to sources used in the research paper. Each citation contains a short annotation, usually about 150 words, which describes and provides evaluative content about the work so the reader can judge the relevance and quality of the work cited.
An annotation is slightly different from an abstract. An abstract is merely a summary of the work whereas an annotation provides more descriptive and critical analysis of the work. An annotated bibliography may contain all or most of the following elements: a brief description of the work, the scope and purpose of the work, the intended audience, relevance or usefulness, helpful features of the work, observations of the author, comments of the reader.
Here's an example of an annotated bibliography from Purdue's Online Writing Lab:
Sample MLA Annotation
Lamott, Anne. Bird by Bird: Some Instructions on Writing and Life. New York: Anchor Books, 1995. Print.
Lamott's book offers honest advice on the nature of a writing life, complete with its insecurities and failures. Taking a humorous approach to the realities of being a writer, the chapters in Lamott's book are wry and anecdotal and offer advice on everything from plot development to jealousy, from perfectionism to struggling with one's own internal critic. In the process, Lamott includes writing exercises designed to be both productive and fun.
Lamott offers sane advice for those struggling with the anxieties of writing, but her main project seems to be offering the reader a reality check regarding writing, publishing, and struggling with one's own imperfect humanity in the process. Rather than a practical handbook to producing and/or publishing, this text is indispensable because of its honest perspective, its down-to-earth humor, and its encouraging approach.
Chapters in this text could easily be included in the curriculum for a writing class. Several of the chapters in Part 1 address the writing process and would serve to generate discussion on students' own drafting and revising processes. Some of the writing exercises would also be appropriate for generating classroom writing exercises. Students should find Lamott's style both engaging and enjoyable.
In the sample annotation above, the writer includes three paragraphs: a summary, an evaluation of the text, and a reflection on its applicability to his/her own research, respectively.