Results are presented for joining of high temperature ceramics such as aluminum oxide, using a high frequency, millimeter-wave source and reactive, glass-based brazes, including joint strength and physical and chemical structure of the joints. The intention of this effort is to provide the capability for production of refractory, high strength joints in ceramics, by using reactive glass brazes, that are then recrystallized to provide a refractory joint. The use of the millimeter-wave source has several, significant advantages in this respect-much better coupling to low loss ceramics (oxides and nitrides) than lower frequency, microwave sources; rapid heating and cooling of joints, and localized delivery of energy in the form of a quasi-Gaussian beam. Beam heating permits localized heating of the joint region only, if desirable, with minimal heating of the rest of the material. Finally, the beam nature of the source permits the use of simple, inexpensive base metal tooling and fixturing for holding pieces to be joined and for applying clamping pressure to these parts.