Quarto is a board game for two players invented by Swiss mathematician Blaise Müller in 1991. It is published and copyrighted by Gigamic.
The game is played on a 4×4 board. There are 16 unique pieces, each of which is either:
tall or short;
red or blue (or a different pair of colors, e.g. light- or dark-stained wood);
square or circular; and
hollow-top or solid-top.
Players take turns choosing a piece which the other player must then place on the board. A player wins by placing a piece on the board which forms a horizontal, vertical, or diagonal row of four pieces, all of which have a common attribute (all short, all circular, etc.). A variant rule included in many editions gives a second way to win by placing four matching pieces in a 2x2 square.
Quarto is distinctive in that there is only one set of common pieces, rather than a set for one player and a different set for the other. It is therefore an impartial game.