The Cornell University Library has defined an annotated bibliography as:
a list of citations to books, articles, and documents. Each citation is followed by a brief (usually about 150 words) descriptive and evaluative paragraph, the annotation. The purpose of the annotation is to inform the reader of the relevance, accuracy, and quality of the sources cited.
In other words you are creating a paragraph that others may read to get a general idea of what your sources are about. The hardest part is being concise with your information. Annotations take practice but once you get the hang of it they are easy. Here are the steps to follow:
A: Talk about the author. (1 sentence)
Is this a professor? Maybe this is a professional in the field? Or is this person a hobbyist? Tell the audience about the author in the first part of the annotation.
B: Explain what the article is about. (1-3 sentences)
Tell the audience what is in the article. This is the most difficult part of the annotation because it requires you to be very succinct. Don’t rewrite the article; just write the base facts and important notes about the article here.
C: Explain how this article illuminates your bibliography topic. (1-2 sentences)
What about this article makes it relevant to your topic? Why did you select it? What pertinent bit of information makes this article stand out among the others?
D: Compare or contrast this work with another you have cited. (1-2 sentences)
How does this specific article relate to another article in your annotated bibliography? Do they agree or not? Why not? What makes them unique?