Sediments are increasingly recognized as both a carrier and a possible source of contaminants in aquatic systems, and they may also affect groundwater quality and agricultural products when disposed on land. Four aspects are covered reflecting the development of knowledge in particle-associated pollutants during the past twenty-five years: – the identification, surveillance, monitoring and control of sources and distribution of pollutants, – the evaluation of solid/solution relations of contaminants in surface waters, – the study of in-situ processes and mechanisms of pollutant transfer in various compartments of the aquatic ecosystems, – the assessment of the environmental impact of particle-bound contaminants, i.e. the development of sediment quality criteria. A final chapter focusses on practical aspects concerning contaminated sediments.