In postal mail, a return address is an explicit inclusion of the address of the person sending the message. It provides the recipient (and sometimes authorized intermediaries) with a means to determine how to respond to the sender of the message if needed.

The return address need not include a sender's name, but should include address or P.O. box details in the same way as the delivery address should. In some countries, the return address is conventionally located in the upper left hand corner of the envelope, card, or label. In the United Kingdom, the return address is usually placed on the reverse of the envelope, near the top.

Businesses often use envelopes preprinted with a return address. Many private individuals have sheets of adhesive labels preprinted with their home address to affix to their correspondence. Charities sometimes include such sheets in mailshots.

The return address is not required on postal mail. However, lack of a return address prevents the postal service from being able to return the item if it proves undeliverable; such as from damage, postage due, or invalid destination. Such mail may thus become dead letter mail.

In some cases, it may be possible to send mail without postage by reversing the roles of the return address and destination address.