The deck consists of 81 cards varying in four features: number (one, two, or three); symbol (diamond, rectangle, or oval); shading (solid, striped, or open); and color (red, green, or blue).

Each card contains 1-3 matching objects, in one of three colors, shapes, and shadings. Twelve cards are laid out, and the user picks three cards that form a set.

A set consists of three cards that are either all alike or all different in each attribute: for instance, if all three cards have the same number of objects, but different shapes, shadings, and colors, then they're a set. If two of the cards have a common attribute that is not shared by the third, they are not a set.