Pex is a twoplayer abstract board game played on a board with pentagonal tiling that was invented by David Bush, an avid Hex player. This game is a member of the connection game family including such game as Hex, Y, Atoll and Crossway.
The pentagonal tiling was taken from the list of 14 known tilings of congruent convex pentagons. Two criteria had to be satisfied:
 Nowhere should more than three edges meet at any vertex.
 The tessellation should be topologically distinct from a hexagonal grid. In other words, not all the interior cells should be adjacent to six other cells.
The only patterns which met both criteria were patterns 11 and 14. In pattern 11, half the interior cells are adjacent to seven neighbors. These are colored yellow. The other interior cells are adjacent to only five neighbors, and are colored green. Pattern 11 was chosen because the playing grid seemed more inherently fair; in other words, the task of connecting the blue borders seemed about as difficult as connecting the red borders. With the pie rule in place, a fair game was virtually guaranteed.
This tesselation was discovered by Marjorie Rice, who deserves equal credit in the creation of Pex.
