The paragraph is the basic unit of composition. It has three main parts: a topic sentence, supporting details, and a concluding sentence. The topic sentence introduces the main idea. Supporting details provide examples, facts, and analysis to develop the topic sentence. The concluding sentence restates the main idea and ties together the paragraph. There are four types of paragraphs: descriptive, narrative, expository, and persuasive. Descriptive paragraphs use details to describe a topic. Narrative paragraphs tell a story. Expository paragraphs explain or define a topic. Persuasive paragraphs aim to convince the reader of a viewpoint.