Paper tickets or the contactless Oyster card can be used for travel. The Oyster Card is a plastic card which stores credit (money and Travelcards) which the owner uses to pay for Underground travel. The user must "charge" (put money onto) their card at a ticket machine. They then touch the card on a yellow reader to pay for their journey. Since its introduction in 2002 it has become very popular with regular travelers, as the prices are much cheaper if you use an Oyster card.