Orientation-dependent reactivity and band-bending are evidenced upon Ti deposition (1–10 Å) on polar ZnO(0001)–Zn and ZnO(000)–O surfaces. At the onset of the Ti deposition, a downward band-bending was observed on ZnO(000)–O while no change occurred on ZnO(0001)–Zn. Combining this with the photoemission analysis of the Ti 2p core level and Zn L₃(L₂)M₄₅M₄₅ Auger transition, it is established that the Ti/ZnO reaction is of the form Ti + 2ZnO → TiO₂ + 2Zn on ZnO(0001)–Zn and Ti + yZnO → TiZn_xO_y + (y − x)Zn on ZnO(000)–O. Consistently, upon annealing thicker Ti adlayers, the metallic zinc is removed to leave ZnO(0001)–Zn surfaces covered with a TiO₂-like phase and ZnO(000)–O surfaces covered with a defined (Ti, Zn, O) compound. Finally, a difference in the activation temperature between the O-terminated (500 K) and Zn-terminated (700 K) surfaces is observed, which is tentatively explained by different electric fields in the space charge layer at ZnO surfaces.