The king is a playing card with a picture of a king displayed on it. The king is usually the highest-ranking face card. In the French version of playing cards and tarot decks, the king immediately outranks the queen. In Italian and Spanish playing cards, the king immediately outranks the knight. In German and Swiss playing cards, the king immediately outranks the Ober. In some games, the king is the highest-ranked card; in others, the Ace is higher. Aces began outranking kings around 1500 with Trappola being the earliest known game in which the aces were highest in all four suits. In the ace–ten family of games such as pinochle and Schnapsen, both the ace and the 10 rank higher than the king.

A playing card is a piece of specially prepared card stock, heavy paper, thin cardboard, plastic-coated paper, cotton-paper blend, or thin plastic that is marked with distinguishing motifs. Often the front (face) and back of each card has a finish to make handling easier. They are most commonly used for playing card games, and are also used in magic tricks, cardistry, card throwing, and card houses; cards may also be collected. Playing cards are typically palm-sized for convenient handling, and usually are sold together in a set as a deck of cards or pack of cards.