Abstract Ecotoxicology is the science devoted to the study of the adverse effects of chemicals on ecosystems structure, functions, and biodiversity. It is a modern discipline, just developed during the last four decades, directly associated to the need to identify, predict, control, and minimize the negative environmental consequences of the recent human industrial development. Ecotoxicology has always been connected to toxicology, and is in part an extension of human/veterinary toxicology to the investigation of effects on wildlife. In parallel, ecotoxicology is also linked to ecology, from both conceptual and methodological viewpoints. Three connected branches should be considered, one covering the assessment and investigation of actual environmental effects including major catastrophes, one dedicated to the development of experimental methods and approaches, and the final one, with predictive character, focusing on the identification, quantification, and communication of the potential hazards of chemicals to the ecosystem.