The gadolinium nitride selenides Gd 3 NSe 3 and Gd 23 N 5 Se 27 are formed by the reaction of gadolinium metal with its triiodide, cesium azide and selenium along with an excess of cesium iodide as flux within seven days at 900°C in torch-sealed evacuated silica ampoules. The dominant phase Gd 3 NSe 3 crystallizes isotypically with Sm 3 NS 3 in the orthorhombic space group Pnma (unit cell: a=1256.71(9)pm, b=398.65(3)pm, c=1318.32(9)pm, Z=4). Thus nitride-centered (Gd 4 ) 12+ tetrahedra are linked via two vertices each forming {[N(Gd1,2)2/1t(Gd3)2/2v]6+}∞1 chains (t=terminal, v=vertex-shared) along [010], which become interconnected by three crystallographically different Se 2− anions. Beside C-type of Gd 2 Se 3 and at least another unknown phase powder diffraction experiments show additional reflections indicating the second nitride selenide Gd 23 N 5 Se 27 . This new compound crystallizes non-centrosymmetrically in the monoclinic space group Pc (unit cell: a=2854.87(19)pm, b=1227.94(8)pm, c=747.62(5)pm, β=94.215(3)°, Z=2). Here, {(Gd14Se40[NGd4]2)20–}∞2 and {([N2Gd6]4Se14)20+}∞2 layers embed the main structural features of isolated [NGd 4 ] 9+ tetrahedra and isolated congonial [N 2 Gd 6 ] 12+ bitetrahedra. Another particularity is the fivefold coordination of the (Gd4) 3+ cations with one short contact to N 3− and four relatively short bonds to four Se 2− anions, respectively.