Formal letter is regarded as a form of letter written for official purposes. The language is strictly formal because it is mostly addressed to someone you do not know. It gives no room for intimate greetings, slangs and abbreviations. It includes two addresses, salutation, title, introduction, body and conclusion. However, titles and some of these parts of a formal letter might vary according to types. Thus, we are going to explain five types of formal letter: sales letter, resignation letter, business letter, permission letter, reference letter.