Abstract: A building block system for building concrete block walls. The system features a main block, a first corner block, a second corner block, a first end block, and a second end block. The blocks interlock with each other via first mating components, second mating components, third mating components, and upper protrusions disposed on various ends of the various blocks. Many of the blocks feature a center aperture, which can engage the mating components and upper protrusions. Generally, the first mating components and upper protrusions can engage the second mating components.