An immersed tunnel is an ideal way of constructing a tunnel across a waterway, as the method relies on water to transport and place the tunnel. The first immersed tunnel was built in 1893, and there are now approximately 180 tunnels of this type that have been built worldwide. This is a relatively low number compared to other forms of tunnel construction, which suggests the field is still in its infancy. In fact, the construction methods draw from many other areas of established engineering practice; it is more the combination of techniques and the marine construction operations that are unusual. With only one or two tunnels opening each year, the knowledge of the technique is restricted to a small community of designers and constructors. With this book, we hope to demystify some of the techniques and broaden the construction industry’s awareness of immersed tunnels.