An Investment Agreement Letter is a contract to set up terms and grounds of the investment of money. Parties involved in the agreement could be two business partners, a client, a company or a government body. An investment is beneficial for any new business. If you are planning for a contract it is important to have an investment contract that represents the interests of everyone involved in it. The investor always wants to confirm that his deal is protected. This letter in general specifies the amount of the investment and the rights of the investor in the project.