The alkylideneamino-aluminium dihalides (R₂C:NAlCl₂)₂(R = Ph or Bu^t) and (Ph₂C:NAIBr₂)_n(n probably = 2) have been prepared from R₂C:NLi and AIX₃(X = Cl or Br); (Ph₂C:NAICI₂)₂ has also been prepared from (diphenylmethyleneamino)trimethylsilane and aluminium trichloride. The trialkylideneamino-derivatives (R₂C:N)₃Al have been prepared from aluminium trichloride and R₂C:NLi (3 molar equiv.). Attempts at the preparation of the dialkylideneamino-derivatives, (R₂C:N)₂AICI, from aluminium trichloride and R₂C:NLi (2 molar equiv.) afforded mixtures of the mono- and tri-alkylideneamino-derivatives. The adduct py,AlCl₃ was formed during the reaction between (Ph₂C:NAICI₂)₂ and pyridine. Details of the i.r. and ¹H n.m.r. spectra of these new moisture-sensitive methyleneamino-compounds are given and discussed, and the mass spectra of two compounds are reported. Four-membered (AIN)₂ ring structures are proposed for the dimeric alkylideneaminoaluminium dihalides. For the monomeric trialkylideneamino-derivatives, the i.r. and ¹H n.m.r. spectra are consistent with Iinear CN⇌Al units, the shape appropriate for maximum N⇌Al dative π-bonding from the methyleneamino-nitrogens to the three-co-ordinated aluminium.