There are at least 4 types of annotations and most of the time your instructor asks you to combine some of the types. If you're doing independent research, think about the type(s) that will suit your purpose best. 

• Descriptive: You describe the source in this type of annotation.. The description includes topics in the work, the scope and time coverage of the topics, and any special features, e.g., appendices.
• Summative: In this type of annotation, you present the main arguments and supporting content of the source, but without any critique. The author's background and credentials may also be included.
• Evaluative or critical: The point of this annotation type is to examine the author's presentation and discuss whether the methodology and reasoning are sound, whether the findings and conclusions contribute to the field, how it compares to other sources, and other evaluative issues. This is often a difficult annotation type for students. Visit the Critical Appraisal and Analysis webpage at Cornell University Library to see the types of questions you might ask.
• Reflective: This type of annotation is your chance to think about the source you've read, and write about how it fits into your body of research and all the other investigation you've done.

Here are some questions to ask yourself as you are writing a reflective annotation:

• How does the source fit into your research?
• Is the source helpful to you, or not?
• What does the source contribute to your understanding of your topic? 
• Does it help you to shape your own argument or stand on the topic?
• Has the source changed how you think about your topic?
• Can you use this source in your presentation, and if so how?

Attribution: W. Todd Kaneko, 2009, The Annotated Bibliography.

You can write annotations with two different sentence structures. For examples, visit the UC Santa Cruz Library website.

1. Phrases. This means writing your annotations with incomplete sentences that start with verbs.
2. Complete Sentences. You can also write your annotation in grammatically complete sentences that have both a subject and verb.

Need help? Then use the library's Ask Us service. Get help from real people face-to-face, by phone, or by email.