Recent projects of very long railway tunnels (from 20 to 50 km or more) at great depth (thousand meters and more) have only emphasized what has been recognized for many years with existing long railway and road tunnels (from 5 to 15 km or more): the work is a complex civil engineering system, to be designed under uncertain conditions with stringent requirements for safety during construction and operation. This report is intended to serve the international tunnelling community as a guideline for planning, design, construction and operation of long and deep tunnels. It recommends an approach or a methodology for solving the major problems involved.