[en] Among ceramic/metal (C/M) joining technologies, the active filler metal method has been studied extensively due to the simple brazing process and excellent joint strength. Active metal elements, typically Ti, are intentionally added to braze alloys to enhance the formation of reaction products between the ceramic and the braze metal at the C/M interface. In the brazing of Al₂O₃ with the Ag-Cu-Ti filler metal, reaction products such as γ-TiO, Cu₂(Ti, Al)₄O, Ti₃(Cu_0.76Al_0.18Sn_0.06)₃O were found, while products such as Ti₅Si₃ and TiN formed in the brazing of Si₃N₄. The presence of reaction layers at the C/M interface influences the interface strength in a complex way. In Cu/Al₂O₃, Co/Al₂O₃, Ni/Al₂O₃, and Cu/diamond systems, maxima of joint strength were observed at some intermediate Ti addition, while the flexural strength decreased substantially with the thickening of the TiO layer in a ZrO₂/Ag-Cu-Sn-Ti system. Thus, composition of the braze alloy (particularly, the content of the active metal), process conditions such as brazing temperature and time, microstructure and mechanical properties of reaction products at the C/M interfaces, interfacial chemistry, and residual stress are primary factors to be studied in order to understand the strengths of the C/M interfaces systematically. In the present and the following papers, evolutions of interfacial microstructures at various brazing conditions, and corresponding interface strengths are reported, respectively, for a ZrO₂/Ag-Cu-Al-Ti system