Abstract: A geometric building and amusement set comprising a plurality of similar block-like pieces each having a generally triangle cross section. The set has three distinctly shaped pieces: a first group of pieces having a generally rectangular male connector formed on one side, a generally rectangular female connector recess formed in another side and proportioned to accept a male connector of an adjacent piece; a second group of pieces formed with only one male connector on one side; and a third group of pieces formed with only the female connector recess on one side. Protuberances are provided on the end portions of the female connector recesses which mate with corresponding recesses formed in the corresponding ends of the male connectors of mating pieces.