An annotated bibliography is a bibliography

Bibliography

Bibliography , as a practice, is the academic study of books as physical, cultural objects; in this sense, it is also known as bibliology...

 that gives a summary of the source.
The purpose of annotations is to provide the reader with a summary and an evaluation of the source. In order to writes a successful annotation, each summary must be concise. An annotation should display the source's central idea(s) and give the reader a general idea of what the source is about.

An annotation should include the complete bibliographic information for the source. It should also include some or all of the following:

• An explanation about the authority and/or qualifications of the author.
• Scope or main purpose of the work.
• Any detectable bias.
• Intended audience and level of reading
• A summary comment

Ideally, an annotation should be between 100 to 200 words.

Indicative annotations

This type of annotation defines the scope of the source, lists the significant topics and explains what the source is about. In this type of entry, there is no attempt to give actual data such as hypotheses, proofs, etc.

Informative annotations

This type of annotation is a summary of the source. An informative annotation should include the thesis of the work, arguments or hypotheses, proofs and a conclusion.

Evaluative annotations

This type of annotation assesses the source's strengths and weaknesses—how the source is useful and how it is not. Simply put, an evaluative annotation should evaluate the source's usefulness.

Combination annotations

Most annotated bibliographies contain combination annotations. This type of annotation will summarize or describe the topic, and then evaluate the source's usefulness.

Writing styles

No matter which writing style is used for annotations, all entries should be brief. Only the most significant details should be mentioned. Information that is apparent in the title can be omitted from the annotation. In addition, background materials and any references to previous work are usually excluded.

Telegraphic

A telegraphic writing style gets the information out quickly and concisely. Maintaining clarity, complete and grammatically correct sentences are not necessary.

Complete sentences

A complete sentences writing style utilizes coherent sentences that are grammatically correct. Subjects and conjunctions are not eliminated even though the tone may be terse. Long and complex sentences are to be generally avoided.

Paragraph

A paragraph writing style utilizes a full, coherent paragraph. This can sometimes be similar to the form of a bibliographic essay. Complete sentences and proper grammar must be used.

Purpose

There are three main purposes behind writing an annotated bibliography. Each purpose can serve anyone in a different manner, depending on what they are trying to accomplish.

Learning about a topic

Writing an annotated bibliography is an excellent way to begin any research project. While it may seem easier to simply copy down bibliographical information, adding annotations will force the researcher to read each source carefully. An annotation requires the source to be critically analyzed, not simply read over.

Formulating a thesis

Any form of research paper or essay will require some form of argument. This is called a thesis

Thesis

A dissertation or thesis is a document submitted in support of candidature for an academic degree or professional qualification presenting the author's research and findings...

. A developed thesis needs to be debatable, interesting and current. Writing an annotated bibliography will give the researcher a clear understanding about what is being said about his/her topic. After reading and critically analyzing sources, the researcher will be able to determine what issues there are and what people are arguing about. From there, the researcher will be able to develop his/her own point of view.

To assist other researchers

Extensive and scholarly annotated bibliographies are sometimes published. The purpose of these annotated bibliographies is to provide a complete and comprehensive overview of any given topic. While a typical researcher may not have their own annotated bibliography published, a search for previously published annotated bibliographies related to their topic could prove very beneficial.