Related: How To Write a Business Proposal Letter (With Template) How to write a proposal letter A clear and influential letter will increase the likelihood of your audience favoring your proposal and moving forward with it. Proposal letters are important because they are normally the first impression your recipient has of you and your business. Related: How To Get a Grant Writing Certification in 4 Steps Why are proposal letters important? Proposal letters can also be sent as a brief precursor to a larger, more-detailed business proposal, like a government grant for a research project. Proposal letters can be used for a variety of endeavors, including small business projects, like requesting a loan or suggesting a new marketing plan to your manager. A proposal letter can introduce an idea to try to convince the recipient to read a full document with supporting information, or it can be the proposal itself. A proposal letter is a professional document that introduces your business ideas to an important recipient who holds a decision-making role.