Historical documents are written records that provide valuable information about past events, cultures, and societies. These documents can include letters, treaties, government records, and personal diaries. They help historians and researchers understand how people lived, what they believed, and how they interacted with one another during different periods in history. Examples of important historical documents include the United States Constitution, the Magna Carta, and the Diary of Anne Frank. Each of these documents offers insights into the values, struggles, and achievements of the time in which they were created, making them essential for studying history.