A new family of quaternary alkali-metal indium selenites, AIn(SeO3)(2) (A = Na, K, Rb, and Cs) have been synthesized, as crystals and pure polycrystalline phases through standard solid-state and hydrothermal reactions. The structures of the reported materials have been determined by single-crystal X-ray diffraction. While AIn(SeO3)(2) (A = Na, K, and Rb) crystallize in the orthorhombic space group, R (3) over barm, with three-dimensional framework structures, CsIn(SeO3)(2) crystallizes in the trigonal space group, P.m, with a two-dimensional structure. All of the reported materials, however, share a common structural motif, a network of corner-shared InO6 octahedra and SeO3 groups. Interestingly, the size of the alkali-metal cations profoundly influences the bonding nature of the SeO3 group to the InO6 octahedra. Complete characterizations including infrared spectroscopy, elemental analyses, and thermal analyses for the compounds are also presented, as are dipole moment calculations. A detailed cation size effect on the framework structure is discussed.