A paragraph is a sentence or group of sentences that support one main idea. It is a series of sentences that are organized and coherent, and are all related to a single topic. In academic writing, a paragraph is often between five and ten sentences long but it can be longer or shorter, depending on the topic. Paragraphs can contain many different kinds of information. A paragraph could contain a series of brief examples or a single long illustration of a general point. It might describe a place, character, or process; narrate a series of events; compare or contrast two or more things; classify items into categories; or describe causes and effects. Regardless of the kind of information they contain, all paragraphs share certain characteristics. One of the most important of these is a topic sentence. A paragraph has three basic parts: the topic sentence, the supporting sentences, and the concluding sentence.