The Oyster card is a form of electronic ticketing used on public transport services within the Greater London area of the United Kingdom. It is promoted by Transport for London and is valid on a number of different travel systems including London Underground, buses, the Docklands Light Railway (DLR), London Overground, trams and some National Rail services.

Oyster is a blue, credit-card-sized stored value card which can hold a variety of single tickets, period tickets and travel permits which must be added to the card prior to travel. It is also a contactless smartcard which passengers must pass over electronic readers when entering and leaving the transport system in order to validate it or deduct funds. The cards may be "recharged" in person from numerous sales points, by direct debit or by online purchase. The card is designed to reduce the number of cash transactions at ticket offices and the number of single paper tickets sold on the London transport network. Usage is encouraged by offering substantially cheaper fares on Oyster than payment with cash.