Idiomorphous crystals of five different polymorphic modifications (a—e) of Tel 4 are simultane-ously grown from solutions of Tel 4 and concentrated HI in methanol by evaporating the solvent at room temperature. (5-TeI 4 is the only stable phase at normal conditions. Phase transformations of a-, ß-, y-and £-TeI 4 to the final stage (5-TeI 4 take place by heating and run through discrete intermediates. The observed graduations lead to a sequence y-, ß-, a-,_e-TeI 4 which indicates "increasing metastability". The crystal structures of a-TeI 4 (trigonal; P3ml; a = 4.228(2), c — 6.684(6) A, Z = 0.5; D v = 5.10 g/cm 3), /3-TeI 4 (orthorhombic; Pn2,m; a = 6.888(2), b = 14.539(3), c = 16.753(4) Ä, Z = 8; D r = 5.03 g/cm 3) and y-TeI 4 (monoclinic; P2,/c; a = 11.199(4), b = 13.599(4), c = 22.158(6) Ä,/3 = 98.10(3)°, Z = 16; D, = 5.05 g/cm 3) are related to the known crystal structure of d-TeI 4 . a-TeI 4 ("Teo.s^") is an isotype of the 2H-CdI : structure with random distribution of Te over the Cd-positions. The crystal structures of ß-, y-and d-TeI 4 contain discrete tetrameric molecules "(TeI 4) 2 (Tel3 + I _)2" which are generated by ordered distributions of Te over 1/4 of the octahedral holes of a 2H-(ß) and a 4H-sequence (y, d) of the nearly close packed iodine layers. A nearly cubic close packing of Iodine atoms is observed in the crystal structure of £-TeI 4 (tetragonal; 14,/amd; a = 16.875(6), c -11.829(5) Ä, Z = 16; D v = 5.01 g/cm 3). The ordered distribution of Te in 1/4 of the octahedral holes leads to tetrameric molecules "(Tel 3 + I~) 4 " in a cubanelike arrangement which, thus far, has been observed only in the crystal structures of TeCl 4 and TeBr 4 . The Madelung Parts of Lattice Energies, MAPLE, of ß-, y-, d-and £-TeI 4 are calculated.