A set of toy building blocks, each block of the set being identical as to size and shape, each block consisting of a single piece in the shape of a cube having two cubic shaped recesses located in two diagonally opposite corners of said block respectively, the remaining six corners of said cube being free of any such recess, each recess having three square faces each parallel to a side of said cube, said faces being equal in dimension and devoid of connecting means, and wherein said dimension is one-half the length of a side of said block, each of said faces and sides being uninterruptedly planar.