The objective of this Guide is to answer the following question: What does an Owner need to know and document for the planning, construction and operation of an immersed tunnel? The Guide will give owners confidence to consider an immersed tunnel as a realistic alternative for crossing waterways and help them achieve the quality and standard of construction they are accustomed to or desire. While an immersed tunnel is a specialist field within civil engineering, its planning, construction and operation follow the same established procedures for any major infrastructure project. This Guide is written with the intention of demystifying the complexities of an immersed tunnel and to help an owner identify the aspects of an immersed tunnel that need particular attention. As such, the Guide is immersed tunnel specific and does not discuss routine construction practices.