Abstract: Stackable and connectable foam building blocks include pairs of parallel side walls and opposite end walls extending between ends of side walls and multiple transverse members extending between the side walls at regular intervals. Each end wall has a U-shaped cutout section at its top to allow concrete flow between cavities of adjacent blocks and for supporting rebars. The upper edge of the end wall defining the lower part of the U-shaped section gradually increases from the outer surface to the inner surface of the end wall to form a downward and inward sloping surface for the lower part of the U-shaped section. Each transverse member includes a pair of structures substantially identical to the end walls. The two structures are positioned back-to-back, such that each cutout surface slopes inward and downward from the middle of the transverse member towards the adjacent cavity and a ridge is formed where the two sloping surfaces meet.