Construction system based on the combined use of blocks designed to lock together. There are three basic blocks, the full, half and knock-out blocks with which any desirable structure can be built. The full block comprises protruding ears (107) and grooves (100). The half block and the knock-out comprise grooves (200 and 304) only. There are standard measurements between groove faces in all blocks and standard measurements between ears in the full block which correspond to the measurements of the groove faces. This provides for a wide array of interbonding positions.