Abstract The Water Framework Directive requires that European Union (EU) Member States ensure that their surface waters are in at least good ecological status by 2015 or at the latest by 2027. The good ecological status objective has been described and operationally defined in the Water Framework Directive. Member States develop their own ecological assessment methods but they must demonstrate that their methods and resulting classifications are comparable to other Member States across the EU. Comparability of assessment results is determined through an intercalibration exercise, the subject of this article. In 2013 The European Commission issued an updated Commission Decision on the results of intercalibration of assessment results across Europe. We present an overview of the process, discuss critical issues and good practices, and recommend approaches for a successful completion of the exercise.