Dwindling timber reserves, combined with short supply of construction time and skilled labor are making concrete block systems an attractive choice for retaining wall construction. These systems are durable, attractive, and require no special tools or skills for installation. Many are self-aligning. There are a number of different types of block systems that use several different methods of interlocking systems. These interlocking connections eliminate the need for mortar and automatically align the block properly, saving time and labor costs. The three types of connection mechanisms are keys, lips and pins.