Underground mines are typically extensive labyrinths that employ many people working over an area of many square miles; extensive analysis of mine-communications systems has identified specific problem areas, in particular the excessive times required to locate key personnel underground, the inadequacy of existing phone systems in terms of capacity and privacy, and the inability to communicate with men on the move with wireless communications, as is taken for granted on the surface. A review is presented of the existing systems, the problem definition, and the various approaches that have been or are being investigated to solve these problems.