Abstract: A molded cement building block having horizontal and vertical pairs of tongue over groove configurations for interlocking with horizontally and vertically adjacent, similarly shaped blocks. The block is formed with two identically shaped side members integrally formed with a central member. A centrally disposed tongue extends longitudinally above the top surfaces of the side elements to form the vertical tongue and is recessed with respect to the bottom surfaces of the side members to form the vertical groove. The horizontal tongue and groove which interlock with adjacent blocks in a course are formed by the central member projecting at one end beyond the ends of the side members and being recessed with respect to the other ends of the side members to form respectively male and female ends in each block.