An invoice is a formal document issued by a seller or service provider to a client requesting payment for goods delivered or services rendered. It serves as both a payment request and a legal record of the transaction. A standard invoice includes the invoice number, issue date, due date, a description of the goods or services provided, the amount owed, payment terms, and payment instructions. For self-employed individuals and freelancers, invoicing is a critical part of getting paid. It establishes a paper trail, sets clear payment expectations, and provides documentation for tax purposes. Invoices differ from receipts: an invoice requests payment before it's made; a receipt confirms payment after.