A paragraph is a group of related sentences that develops a single main idea. It typically includes a topic sentence stating the main idea and supporting sentences that provide details, examples, or evidence. A good paragraph has unity around a clear topic, coherence through logical connections between ideas, and variety in structure. The four main types of paragraphs are descriptive, which describe a person, place, or thing; informative, which explain an idea or facts; narrative, which tell a story or event; and persuasive, which aim to influence the reader.