Amorphous TiO2 materials, layers and powders, have been produced by different preparation techniques. The layers have been subjected to electron diffraction and the bulk powders to X-ray diffraction experiments. Three-dimensional structure models consistent with the experimental structure functions have been constructed by reverse Monte Carlo simulations. Partial distribution functions, interatomic distances and coordination numbers have been extracted from the model atomic configurations. The atomic arrangement in all amorphous TiO2 materials investigated has been found to resemble that occurring in brookite, a crystalline modification of TiO2, and to be well described as an assembly of short, staggered chains of Ti-O octahedra. The crystallization behaviour of amorphous TiO2 materials has also been discussed.