NaBH4·2H2O and NaBH4 were studied by single-crystal X-ray diffraction and vibrational spectroscopy. In NaBH4·2H2O, the BH4- anion has a nearly ideal tetrahedral geometry and is bridged with two Na+ ions through the tetrahedral edges. The structure does not contain classical hydrogen bonds, but reveals strong dihydrogen bonds of 1.77-1.95 Å. Crystal structures and vibrational spectra of NaBr·2H2O and NaBH4·2H2O reveal many similarities. The unit cell volume of NaBH4·2H2O increases linearly with temperature between 200 and 313 K. At 313-315 K, the hydrate decomposes into NaBH4 and H2O, which react to release hydrogen.