Learn what a letter of agreement is and how to write one, including a template and example to help you get started crafting your own. A Letter of Intent is a written document that serves as an initial agreement between two parties concerning the terms of a possible purchase or transaction.A contract consists of a legally binding agreement or promise between parties. A letter agreement is a written legal document that is made between two parties who want a simple way to make their discussions of a transaction official. Erite out what your goals are for the agreement. Create a Letter of Agreement (LOA) using our free DIY printable template. Remind someone of their legal duties to you before initiating legal proceedings.