There are many different types of letters that can be written, but some of the most common types include personal letters, business letters, cover letters, and thank-you letters. Personal letters are written to friends, family members, and other people with whom the writer has a personal relationship. Business letters are written for professional purposes and are often used to communicate with clients, customers, and other businesses. Cover letters are typically included with job applications and provide additional information about the applicant's qualifications and experiences. Thank-you letters are written to express gratitude and appreciation for a variety of reasons, such as receiving a gift or being offered a job.