Two types of clusters, [Ag(Se₂P(OR)₂)]_n (R = Et, n = ∞, 1a; R = Prⁱ, n = 6, 1b) and Ag₁₀(μ₁₀-Se)[Se₂P(OR)₂]₈ (2a, 2b) were obtained from the reaction of stoichiometric amounts of Ag(CH₃CN)₄PF₆ and NH₄Se₂P(OR)₂ in (C₂H₅)₂O at −20 °C. These new silver(I) clusters containing diselenophosphate (dsep) ligands were characterized by elemental analysis, NMR spectroscopy, fast-atom bombardment mass spectrometry (FAB-MS) for 2, and, in the case of 1b, and 2a, by X-ray crystallography. The structure of 1b reveals a hexameric aggregate {Ag[Se₂P(OPrⁱ)₂]}₆ where six silver atoms are located at the corners of a pseudohexagonal prism alternating with selenium atoms in two Ag₃Se₃ rings interconnected vertically by the P–Se bridges of the dsep ligands but not by additional Ag–Se bonding. The dsep ligands are organized in a paddle-wheel fashion about an Ag₆Se₆ pseudohexagonal prismatic core. The decasilver clusters 2 contain an encapsulated selenium atom in a distorted, cis-bicapped trapezoidal-prismatic geometry and are surrounded by eight dsep ligands having three different types of coordination pattern. Furthermore, the hypercoordinated selenide ion, Se²⁻, in 2 was unequivocally identified by the solution ⁷⁷Se{¹H} NMR spectrum with a chemical shift centered at −1396 ppm.