Goal
Own more boxes than your opponent once every line on the grid has been drawn.
Your turn
Draw one line segment between two adjacent dots. If that line completes the fourth side of a box, you claim it — mark it with your color — and take another turn. A single line can complete two boxes at once if it closes both their fourth sides, earning you an extra turn either way.
Play continues until every box is claimed. Most boxes wins (ties are possible on even boards).