This technical guidance document is intended as a basic introduction to water quality monitoring and to guide readers to the most relevant detailed guidebooks in this series. It is intended for scientists and technicians who do not have specialised knowledge or experience in water quality monitoring and need a general overview of the key aspects and complexities of establishing a water quality monitoring programme. It highlights the need for understanding the hydrological and ecological functioning of water bodies when planning a sampling and analysis programme. Brief guidance is given for choosing monitoring approaches and water quality parameters that will provide meaningful and useful data for management and policy making.