Strong metal-ceramic bonds require thermodynamic adhesion with the formation of new phases at the interface when the system is reactive, or without the formation of new phases when the: system is non-reactive. The copper-alumina system can be reactive or non-reactive depending on the oxygen content in the atmosphere and/or in the copper. The non-reactive/reactive transition was determined and corresponded to an oxygen partial pressure of about 4.9 x 10(-3) Torr. For solid start bonding, in non-reactive conditions, the fracture strength of the bonds increased as the oxygen partial pressure tended towards this transition value. For reactive conditions, the growth of CuAlO2 induced a high interfacial fracture energy. For metal-alumina brazing, to enhance welting, alumina was sprayed with copper powder in air and subsequently brazed using Ag-28 wt% Cu alloy. The surface-active effect of oxygen present in the Cu-Cu2O deposit favours the wetting of alumina by the AgCu brazing alloy, as well as adhesion, because of the segregation of silver at the metal-ceramic interface associated with the formation of Ag-O clusters.