The binary compound Sr3In11 (SrIn3.667) was synthesized and structurally characterized by X-ray diffraction experiments. It crystallizes in the orthorhombic La3Al11 structure type (space group Immm, Z = 2; a = 4.9257(6), b = 14.247(2), c = 11.212(2) Angstrom). The crystal structure of Sr3In11 bears features of the monoclinic EuIn4 structure, which is adopted by SrIn4, and the prominent tetragonal BaAl4 structure. Sr3In11 is stable until 550 degreesC. At higher temperatures it decomposes peritectically into SrIn2 and In. Structural stability and bonding properties of Sr3In11 were investigated by first principles calculations and compared to SrIn4 in the monoclinic EuIn4 and the tetragonal BaAl4 structure. All three structures consist of a three-dimensional, polyanionic, network formed by In atoms and Sr cations encapsulated in cages. For the BaAl4-type SrIn4, In-In network bonding is perfectly optimized. In contrast, the networks of EuIn4-type SrIn4 and Sr3In11 appear hypo- and hyperelectronic, respectively. The formation of Sr3In11 with a composition close to 1:4 and the nonexistence of BaAl4-type SrIn4 is explained by a delicate interplay of size and electronic factors governing structural stability in the In-rich part of the Sr-In system.