The new selenide Cs2Ge3In6Se14, featuring its own structure type with germanium in mixed-valence states, is discovered via a solid-state reaction at 1173 K. The compound crystallizes in the R (3) over bar m space group with a = 7.9951(6) (A) over circle and c = 41.726(4) (A) over circle. Two adjacent condensed layers of InSe4 tetrahedra are linked by a [Ge2+Se6] octahedron into a double slice that is further stacked along the c direction with a packing sequence of ...abca... through the [Ge23+Se6] dimer via its Ge-Ge metallic bond. The coexistence of Ge2+/Ge3+ and Ge-Ge metallic bonding has been confirmed by XPS and ELF analyses, respectively. More interestingly, although sharing many structure similarities, Cs2Ge3In6Se14 and our previously reported Cs2Ge3In6Te14 reveal a R (3) over barm to P (3) over bar m1 structure transformation with a tripled c parameter. Single-crystal diffraction data and a thorough structure survey of related compounds point out that such a transformation is driven by the size preference of the [Ge(2)Q(6)] dimer. The title compound possesses a band gap of 2.08 eV and shows photodegradation of RhB under visible light that is more efficient than that for the commercial P25.