The Zener cards were a deck made up of five simple symbols. The five different Zener cards are: a hollow circle (one curve), a Greek cross (two lines), three vertical wavy lines (or "waves"), a hollow square (four lines), and a hollow five-pointed star. There are 25 cards in a pack, five of each design.

In a test for ESP, the person conducting the test (the experimenter) picks up a card in a shuffled pack, observes the symbol on the card, and records the answer of the person being tested for extrasensory perception, who would guess which of the five designs is on the card in question. The experimenter continues until all the cards in the pack have been tested. Poor shuffling methods can make the order of cards in the deck easier to predict. The cards could have been marked and manipulated. In his experiments, J. B. Rhine first shuffled the cards by hand but later decided to use a machine for shuffling.