Amorphous tantala (a-) is an important optical material used in a number of high-precision optical applications, including gravitational wave interferometry. In this paper, we study the structural changes that occur in amorphous ion-beam sputtered coatings during an annealing treatment by means of a synchrotron radiation scattering experiment . The scattering signal is measured as a function of time on a large range of the Q-space. X-Ray diffraction and Rietveld analysis are used to study crystallization during the annealing treatment, whereas pair distribution function (PDF) analysis allows to inspect the structural changes occurring during the amorphous–to-crystalline transition. Our findings indicate that several structural rearrangements occur in parallel, namely a first quick establishment of a “backbone” structure in the cationic substructure appearing on a rather extended range (up to 100 ), followed by a progressive rearrangement of the short-range structure in which Ta-Ta correlations evolve in parallel with Ta-O correlations. At longer times, long-range correlations appear, marking the onset of crystallization.