From the box cover:

"Bolero - a tactical game for two.

A rousing, ingeniously simple game, where winning demands all your acuity and maneuvering skills."

Players take turns to place their markers on the board. Both players have 64 markers numbered 1-4, 16 of each. The board is a 4x4 grid of 2x2 squares numbered 1-4. The played marker always goes to a square with a same number.

The player who first creates

1. a row of 4 same numbers horizontally, vertically or diagonally,

2. a row of 4 different numbers horizontally, vertically or diagonally or

3. a 2x2 square of 4 different numbers

with his own markers wins the game.