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The thermal decomposition of the hydrazine adducts R3Al←NH2–N(H)CMe3(1a, R = CMe3; 1b, R = Me) was investigated. Compound 1aafforded the hydrazide [(Me3C)2Al–N(H)–N(H)–CMe3]2(2) upon heating to 155 °C. Compound 2is dimeric in the solid state with a four‐membered Al2N2heterocycle in its molecular core. Heating of 2to 190 °C gave the drum‐like imidoalane [Me3CAlNH]6(4) in which the Al and N atoms occupy the vertices of a hexagonal prism. This reaction is believed to proceed via the dimeric amide [(Me3C)2Al–NH2]2(3) that was isolated in small quantities from a mixture obtained at a slightly lower temperature. Adduct 1b, which is sterically less shielded than 1a, decomposes readily at room temperature to yield an unprecedented Al–N cage compound, [Me2Al–N(H)–N(H)CMe3]2[MeAl–N(CMe3)–NH] (5), with a norbornane‐like arrangement of three Al and four N atoms, and a hydrazinediido group in the bridging position. Heating of 5gave, with the release of methane, the tetraaluminum compound [MeAlN(H)–NCMe3]4(6) in which four hydrazinediide moieties are bridged by AlMe groups. Heating of 6resulted in the gradual degradation of the N–N bonds and the formal release of 1 or 3 equiv. of nitrene, N–H, to give the unique cage compounds (MeAl)4[N(H)–NCMe3]3(NCMe3) (7) and (MeAl)4[N(H)–NCMe3](NCMe3)3(8). The structures of compounds 6–8may be derived from Al4N4cubes in which a number of edges (four, three or one) are bridged by nitrogen atoms of hydrazinediido groups.