A bill of lading (also known as a B/L or BOL) is a mandatory document issued by a carrier (or their agent) to a shipper that details the type of shipment, quantity, and destination. Although the phrase was previously limited to seaborne transportation, a bill of lading can now be used for any sort of commodities transportation. Bills of lading are one of three important documents used in international trade to ensure that exporters receive payment and importers receive goods.

The other two documents are an insurance policy and an invoice. While a bill of lading can be negotiated, neither a policy nor an invoice can be assigned. Bills of lading differ from waybills in international trade outside the United States in that the latter are not transferable and do not confer title. Nonetheless, the Carriage of Goods by Maritime Act 1992 of the United Kingdom allows "all rights of litigation under the contract of carriage" to the legitimate holder of a bill of lading or the consignee under a sea waybill or a ship's delivery order.

A bill of lading must be transferable and has three purposes:  

• It is a conclusive receipt, i.e. an acknowledgement that the goods have been loaded; 
• It contains, or evidences, the terms of the carriage contract; and 
• It serves as a document of title to the commodities, subject to the nemo dat rule.

Incoterms such as CIF, FOB, or FAS are commonly used in export transactions, requiring the exporter/shipper to deliver the goods to the ship, whether onboard or alongside. Nonetheless, the carrier or a third-party stevedore will normally do the loading.

Although there is evidence of receipts for goods loaded aboard merchant vessels dating back to Roman times, and the practice of recording cargo aboard ship in the ship's log is almost as old as shipping itself, the modern bill of lading only became common with the growth of international trade in the medieval world.

The rise of mercantilism (which gave rise to other financial inventions like the charterparty or carta partita, the bill of exchange, and the insurance policy) necessitated the creation of a title document that could be traded in the same way that the products themselves could. This new trade route resulted in the creation of the bill of lading in its current form.

Both the words "lading" and "loading" are derived from the Old English word hladan. The term "lading" refers to the loading of cargo onto a ship. The Dutch word "lading" has the same meaning (freight, cargo, a quantity of transportable items) as the English "bill of lading," but it is not limited to shipping.

The Carriage of Goods by Sea Act 1992 of England states that the term "bill of lading" includes a "received-for-shipment" bill of lading issued by, for example, a freight forwarder or a storage depot/warehouse. A "combined bill of lading" may be issued by a carrier who, for example, gathers products from a factory and delivers them to a ship via multi-modal transportation.