This document provides guidance on writing effective letters for business or contractual communication. It outlines the key elements that should be included in a letter such as identifying the sender and recipient, including a reference number and date, clearly stating the subject or purpose, and having a main body that communicates the key information along with a clear conclusion. The document also discusses styles of address, signatures, attachments and copying other relevant parties. Well-structured letters that follow these guidelines can help formalize important communications and record decisions or issues for traceability.