Abstract: There is provided a building block (10) comprising a rectangular parallelepiped having three pairs of opposing surfaces (12 and 14, 16 and 18 and 20 and 22), each pair of opposing surfaces being provided with one or more identical pairs of interlocking formations (24 and 26), whereby two such building blocks (10) may be arranged with one of a pair of opposing surfaces of a first of the blocks in interlocking engagement with one of any of the three pairs of opposing surfaces of the other of the blocks. There is also provided a corner block (100) for use with a building block (10) of the type previously described, the corner block (100) subtending in included angle and being provided with one or more formations (118) on each of its surfaces (102-116) whereby the corner block (100) may be arranged with one of its surfaces (102-116) in interlocking engagement with one of at least one of each pair of opposing surfaces (12 and 14, 16 and 18 or 20 and 22) of said building block (10).