Aluminum hydride (alane; AlH3) has been identified as a leading hydrogen storage material by the US Department of Energy. With a high gravimetric hydrogen capacity of 10.1 wt.%, and a hydrogen density of 1.48 g/cm(3), AlH3 decomposes cleanly to its elements above 60 degrees C with no side reactions. This study explores in detail the thermodynamic and spectroscopic properties of AlH3; in particular the alpha, alpha' and gamma polymorphs, of which alpha'-AlH3 is reported for the first time, free from traces of other polymorphs or side products. Thermal analysis of alpha-, alpha'-, and gamma-AlH3 has been conducted, using DSC and TGA methods, and the results obtained compared with each other and with literature data. All three polymorphs were investigated by H-1 MAS-NMR spectroscopy for the first time, and their Al-27 MAS-NMR spectra were also measured and compared with literature values. AlH3 center dot nEt(2)O has also been studied by H-1 and (27)AI MAS-NMR spectroscopy and DSC and TGA methods, and an accurate decomposition pathway has been established for this adduct. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.