Customs is an authority or agency in a country responsible for collecting tariffs and for controlling the flow of goods, including animals, transports, personal effects, and hazardous items, into and out of a country. Traditionally, customs has been considered as the fiscal subject that charges customs duties and other taxes on import and export. In recent decades, the views on the functions of customs have considerably expanded and now covers three basic issues: taxation, security, and trade facilitation.

Bag tags, also known as baggage tags, baggage checks or luggage tickets, have traditionally been used by bus, train, and airline carriers to route checked luggage to its final destination. The passenger stub is typically handed to the passenger or attached to the ticket envelope: to aid the passenger in identifying their bag among similar bags at the destination baggage carousel; as proof—still requested at a few airports—that the passenger is not removing someone else's bag from the baggage reclaim hall; and as a means for the passenger and carrier to identify and trace a specific bag that has gone astray and was not delivered at the destination. The carriers' liability is restricted to published tariffs and international agreements.