STATE of the art of joining structural ceramics has been critically assessed both from scientific and technological viewpoint. Commonly used, unconventional and emerging joining techniques and concepts have been identified, and potential opportunities for further development outlined. Pressure-assisted diffusion bonding, glass and eutectic joining, in situ joining by ceramic processing (nitridation), vapor-deposition, molecular adhesion, etc. are some of the joining concepts discussed.
   In broad terms, joining of structural ceramics can be accomplished by processes utilizing temperatures in excess of melting temperature, down to those relying on room temperature processing. Solid, liquid or vapor phases can serve as adhesive donors.
   The effects of residual stresses on the mechanical reliability of ceramic joints has also been reviewed. High toughness is one of the key requirements; similar concepts apply to toughening of the joints as those developed for composite ceramics.
   A unified theory of molecular adhesion and mechanical strength is as yet lacking, but recent theoretical developments suggest that adhesion of solids might be regarded as the inverse of fracture phenomena. It is suggested that concerted efforts of scientific and engineering communities are required to achieve technological breakthroughs.