S3T (Sets of Three) is a game that is simultaneously simple in principle but potentially complex to play. The goal is to select three card from the play surface that comprise a set.

Cards have four charactistics (shape, color, fill and count) with three variations each. Shape can be either a circle, square or triangle. Color can be either red, green or blue. Fill can be either empty, shaded or filled. Count can be one, two or three shapes on a card.

A set is defined as three cards in which a specific characteristic is the same (e.g. each card has a single circle) or the characteristic is different for each card (e.g. red shape, green shape, blue shape). If any characteristic is the same in two of the three cards, then the cards do not constitute a set. e.g. 1 empty red circle, 1 empty red triangle, 1 empty blue square. In this case, only two cards are red. They either all need to be red or they all need to be a different color.