The aim of this book is to provide information on the planning, design, construction and operation of seawater systems used in aquaculture. The first edition of this book appeared in 1989. Its success and a number of developments, especially in the field of computer calculations and automation, made a second edition useful. The term seawater system is interpreted broadly here: it covers salinities from freshwater to brines. In that respect, the book is of value for anybody working with land-based aquaculture systems. Specific chapters dealing with seawater have to do with site considerations (Chapter 3), seawater sources (Chapter 4) and material selection (Chapter 8). The second chapter after the introduction deals with problem definition and setting requirements for water quality. The part on growth modelling is especially more elaborate in this second edition. Subsequent chapters deal with design of piping and pumps, water treatment like removal of suspended solids, heating and cooling, aeration and disinfection. Small chapters are devoted to control systems and water recycling. In the last chapters, general considerations are given for construction and operation of different types of systems. Very convenient are a number of appendices in which a bibliography of a number of specific subjects is given. Reference to internet sources is a must for a book published in the third millennium although the most interesting sites are not freely accessible. As in the first edition, many examples of calculations are given which makes the book very useful for educational purposes. In general, the information is easy applicable in practice. What puzzles me somewhat is why the publisher has not tried to integrate this book with that from Timmons and Losordo on "Aquaculture water reuse systems: engineering design and management". These books cover a lot of common ground and would together integrate the whole field of design of tank-based aquaculture systems. A general remark on engineering books for aquaculture is that the focus is mainly on the hardware and the water treatment processes. However, information on waste production (or oxygen consumption) and water quality limits is just as important for the final result of the design process as the engineering of the treatment process. In this respect, engineering for aquaculture differs, for example, a lot from that of a sewage treatment plant for which the waste production profile and the water quality requirements can be covered in a few pages. Taking the above into account, this book is still a very worthwhile possession for anybody interested in the design of systems for aquaculture.