A topic sentence is a statement that expresses the main idea of a paragraph. It typically appears at the beginning of the paragraph and sets the tone for the information that follows. By clearly stating the main point, a topic sentence helps readers understand what to expect and provides a focus for the paragraph's content. In academic writing, a strong topic sentence is essential for clarity and coherence. It often includes a specific subject and a controlling idea that guides the discussion. This structure allows writers to organize their thoughts effectively and helps readers follow the argument or narrative more easily.