List of business letters.

1. Letter of inquiry
2. Letter of complaint
3. Letter of recommendation
4. Letter of resignation
5. Letter of introduction
6. Letter of apology
7. Letter of appreciation
8. Letter of invitation
9. Letter of confirmation
10. Letter of agreement

Formal Business Letters

- Application Letter
- Acceptance Letter
- Resignation Letter
- Cover Letter
- Reference Letter
- Letter of Recommendation
- Letter of Intent
- Letter of Inquiry
- Letter of Complaint
- Letter of Explanation
- Letter of Apology
- Sales Letter
- Letter of Credit
- Letter of Guarantee
- Letter of Agreement
- Memorandum of Understanding (MOU)

Semi-Formal Business Letters

- Business Introduction Letter
- Thank-You Letter
- Congratulatory Letter
- Sympathy Letter
- Invitation Letter
- RSVP Letter
- Networking Letter
- Follow-Up Letter
- Proposal Letter
- Query Letter
- Endorsement Letter
- Testimonial Letter

Informal Business Letters

- Email
- Instant Message
- Social Media Post
- Text Message
- Memo
- Meeting Notes
- Progress Report
- Performance Review

Specific Purpose Business Letters

- Credit Card Application
- Loan Application
- Insurance Claim
- Tax Return
- Invoice
- Purchase Order
- Quotation
- RFP (Request for Proposal)
- RFI (Request for Information)
- Due Diligence Request
- Merger and Acquisition Proposal