For over 70 years, the 18 previous editions of Clay’s Handbook of Environmental Health have helped both students and practitioners of environmental health throughout the world understand the concept of environmental health and its practical implementation within a variety of management and administrative systems. Clay has justifiably become the informational bedrock of environmental health. A new edition is always eagerly awaited. This is particularly the case for the nineteenth edition, the first of both a new century and a new millennium. A rapidly changing world demands that environmental health practitioners keep abreast of change and this new edition contains much new material which reflects the problems and pressures that face them today. Old problems sit juxtaposed with new problems and understanding them, and being able to apply solutions to their resolution, remains a constant need for environmental health practitioners.