An internal invoice is an accounting document used by a business to record sales transactions taking place between two divisions of the same company. It helps businesses keep track of the goods and services they are providing, as well as any associated expenses such as shipping and handling fees. Internal invoices provide a detailed record of all transactions within the same organization, allowing a business to better manage its finances and budgeting. With this key tool, businesses can easily monitor and control their expenditures – ensuring efficient operations and profitable results.