In effecting a joint between two optical fibres an elongate gauge having a cross-sectional shape and size corresponding to that of each of the optical fibres to be jointed is laid on a substantially flat surface of a soft, substantially non-resilient metallic body, e.g. annealed copper, and is pressed into the surface to form in, and between two edges of, the surface a groove of a substantially complementary cross-sectional size. The gauge is removed and the two optical fibres are aligned in the groove so formed in such a way that neighboring ends of the optical fibres substantially abut. A second body having a flat surface is applied to the grooved surface in such a way that its flat surface is in interfacial contact with the grooved surface, and the two bodies are secured together.