The renewed interest in transition metals diborides, classified as ultra high temperature ceramics, for applications at high temperature or in highly aggressive environments has given rise in recent years to an increasing number of research projects particularly devoted to the study of their interfacial characteristics when placed in contact with liquid metals and alloys, which complement and upgrade the limited number of older investigations. This paper critically reviews these systematic studies, addressing both basic (wettability, interfacial tension and phase equilibria determination) and application (joining by brazing) aspects. Particular reference is made to studies aimed at elucidating the role that dissolution, chemical reactions, additions of active metal elements to the molten matrix have in the wetting process and on the solid-liquid adhesion in relation to the mechanical characteristics of brazed joints.