The thin-film growth of semiconducting organic molecules, and the molecular interactions and processes therein, for application in organic electronics has been a topic of great interest. Here, we will present our investigations on the thin-film growth of tetracene, a polyaromatic hydrocarbon, whose simple structure belies the complex nature of growth revealed by synchrotron X-ray scattering. Although tetracene is structurally very similar to pentacene, we find that the nature of the thin-film growth on SiO2 of tetracene is quite different from that of pentacene. At a substrate temperature of T_s ~ 30 °C, we observe two unusual phenomena. First, using in situ X-ray reflectivity at the anti-Bragg condition, we observe a transition from 3D island growth to 2D layer-by-layer growth of tetracene as the growth rate is increased. We use ex situ atomic force microscopy to determine that upward transport drives 3D island growth. The transition from 3D growth to 2D growth occurs when the rate of admolecule attachment at the tetracene island/SiO2 substrate edges, which is related to growth rate, effectively outcompetes the rate of upward step-edge transport. Second, using in situ grazing incidence X-ray diffraction, we observe a transition from growth of only a thin-film phase to growth of a bulk phase. We observe that the bulk phase appears at lower thickness and that there is a lower contribution of the thin-film phase for slower growth rate than for faster growth rates. This is due to significant reorganization at slower growth rates, resulting in molecules traversing upwards on islands and escaping the influence of the substrate and relaxing into the bulk phase. Furthermore, we find that at T_s ~ 0 °C, the transition from 3D to 2D growth occurs at a much lower growth rate than at T_s ~ 30 °C, and we observe a lack of evidence for bulk-phase growth. This suggests that the rate of upward transport is suppressed at lower temperatures. Finally, we find that even by matching the surface energy of the substrate (with a pre-deposited layer of pentacene) and tetracene, there is still significant upward transport, although there is less than on pristine SiO2.