Building blocks include a tongue and groove on each block that allow the blocks to be placed in a way that interlocks the tongue and groove of one block with the corresponding groove and tongue, respectively, of another block facing the opposite direction. In a first embodiment, the same building block that has a decorative front face is used for both sides of the wall, resulting in a wall with opposed finished surfaces. In a second embodiment, a first plurality of blocks that have a decorative front face are used for one side of the wall, while a second plurality of blocks that have a thicker and non-decorative face are used for the other side of the wall, with the first and second plurality of blocks interlocking back-to-back via their respective tongues and grooves. Both types of blocks can be made using the same concrete form.