ESDU 03004 is a practical guide to the current state of knowledge relating to fouling in cooling systems using seawater. Developed under the guidance of the Oil Industry Fouling Working Party@ its objective is to provide the designer and the operator of both onshore and offshore equipment with a ready User Guide to the occurrence@ the mechanisms and the mitigation of seawater fouling in these systems. Introductory material on seawater as a coolant includes information on seawater composition and its physical properties. Guidance is given on the selection of seawater cooling system type@ noting the advantages and disadvantages of direct and indirect systems and describing a common application of each type. The various types of fouling (crystallization@ corrosion@ biological and suspended solids) and the parameters that affect them are described. Practical design guidelines to minimise fouling are given@ such as those for design velocities in tubular heat exchangers with tubes of various materials. Practical guidance on the all-important matter of materials selection is then provided which underpin the recent shift towards the use of titanium rather than copper alloys. System design considerations to handle and minimise seawater fouling are reviewed@ such as the effect of enhancement on one side of a heat exchanger on the parameters that control fouling (that is@ velocity and temperature) on the other side of the exchanger. A wide range of measures available for mitigation@ control and on-line removal of fouling are then reviewed. Guidance on cleaning of fouled heat exchangers is provided@ and a brief review is given of some novel applications@ including air-conditioning and Ocean Thermal Energy Conversion (OTEC). An extensive list of selected references is given@ and data are provided for the physical properties of seawater required for many heat exchange calculations. The EXPRESS program can be used to identify designs of tubular heat exchangers that will operate within limitations of tubeside flow velocity and wall temperature for minimum seawater fouling.