To mitigate the ecological impacts of dams upon rivers, restoration projects are focusing on implementing environmental flow regimes to improve ecosystems' health. In Europe, the water requirements for river ecosystems improvement are receiving increasing attention in water supply planning, namely within the Water Framework Directive, which provides a general framework for river protection. Because the protection or restoration of environmental flows necessarily entails trade-offs with other potential uses of water, it is important that the water requirements of a river ecosystem be defined using best-available scientific knowledge. Until now, several methodologies have been used to formulate environmental flow requirements downstream of dams in European rivers, ranging from simple use of hydrological records to establish minimum and flushing flows, to modelling procedures linking changes in river discharge with ecological responses. However, no set of techniques or conceptual framework methodology has been accepted without reservations. This paper describes a integrated procedure for establishing environmental flow regimes in rivers and presents the results of preliminary applications in Portugal. The procedure comprises several steps – collection of background information, selection and sampling of representative river reaches, formulation of environmental flow regimes by means of different methods, field evaluation of the different flow regimes by a multi-disciplinary team of scientists, proposal of an environmental flow regime, monitoring and adaptation – and can be tailored according to available time and financial resources