This document provides an overview of different types of letters and their formats. It begins with defining a letter and discussing the importance of letters. It then covers the introductory components of a letter including the heading, address, date, salutation, and body. The document discusses the classification of letters into formal and informal letters. It provides examples of different types of formal letters including business letters, letters of application, and official letters. It also covers informal letter types such as social letters and friendly letters. The document concludes with providing samples of different letter formats and structures.