International and European standards relevant to algal-based monitoring have been developed by the International Standards Organisation (ISO) and the Comite Europeen de Normalisation (CEN). This work has been given new impetus by the publication of the EU Water Framework Directive (2000/60/EC), which requires the use of CEN and ISO standards where available. Standards addressing diatom sampling and analysis, macrophyte survey, algal survey and phytoplankton analysis are all either published or under development by CEN. There is also a standard under development dealing with quality assurance of ecological assessments in the aquatic environment. Together, these standards should ensure that robust data are collected that can be used for intercalibrations between Member States.