The Penny Black was the world's first adhesive postage stamp used in a public postal system. It was first issued in the United Kingdom (referred to in philatelic circles as Great Britain), on 1 May 1840, but was not valid for use until 6 May. The stamp features a profile of Queen Victoria.

In 1837, British postal rates were high, complex and anomalous. To simplify matters, Sir Rowland Hill proposed an adhesive stamp to indicate pre-payment of postage. At the time it was normal for the recipient to pay postage on delivery, charged by the sheet and on distance travelled. By contrast, the Penny Black allowed letters of up to 1⁄2 ounce (14 grams) to be delivered at a flat rate of one penny, regardless of distance.