The use of tunnels to improve transport networks by traversing increasingly large and difficult physical obstacles is acclerating. In developed urban areas, tunnels are also being used to ease congestion and reduce pollution by putting traffic underground. In parallel with new construction, many older tunnels are being refurbished, including ventilation improvements to enhance safety in both the normal operational environment and in emergency, particularly fire, situations. Meanwhile the ability to design efficient and safe ventilation systems for increasiungly long tunnels is being developed by the advances in analysis, calculation and simulation techniques using CFD techniques. The papers from this ninth international conference held at Aosta Valley, Italy, in October 1997 cover aspects of both road and rail tunnels.