A card game is played with a deck (common in the US), or pack (common in the UK), of cards intended for that game. The deck consists of a fixed number of pieces of printed cardboard known as cards. The cards in a deck are identical in size and shape. Each card has two sides, the face and the back. The backs of the cards in a deck are indistinguishable. The faces of the cards in a deck may all be unique, or may include duplicates, depending on the game. In either case, any card is readily identifiable by its face. The set of cards that make up the deck are known to all of the players using that deck.

Although many games have special decks of cards, the 52 card pack is known as the standard deck, and is used in a wide variety of games. It consists of 52 cards, each card having a suit (one of spades, hearts, diamonds and clubs) and a rank (a number between 2 and 10, or one of jack, queen, king and ace). For any combination of one suit and one rank, there is exactly one card in the standard deck having that suit and rank. In addition to games that use the standard deck, there are also games that use some modification of the standard deck, for example excluding all cards of rank lower than some rank (e.g., a pinochle deck), or adding a special card, joker, to the standard deck. Many European regions have their own variants of the standard deck having different names and imagery for suits, or having a different set of ranks in the cards.