Fillomino is played on a rectangular grid with no standard size; the internal grid lines are often dotted. Some cells of the grid start containing numbers, referred to as "givens". The goal is to divide the grid into polyominoes (by filling in their boundaries) such that each given number n in the grid is part of an n-omino and that no two polyominoes of matching size (number of cells) are orthogonally adjacent (share a side).