A short web document by Ralph Griswold introducing 5x5 pantactic squares, two-color grid patterns in which every 2x2 subpattern is different. It explains the hexadecimal labeling of the sixteen 2x2 subpatterns, the 800 essentially different squares, and their lack of symmetry. It also covers limits on connected paths and blocks, and how basic blocks can tile into larger repeating patterns, with two tiling examples. It closes with open questions about larger, non-square, and multi-color pantactic designs.