The monitoring of environmental effects is an important element of the regulatory framework for genetically modified organisms (GMO) in the European Union and Switzerland. The aim of GMO monitoring is to detect potential adverse effects of GMOs and their use on human health and the environment and – if necessary – to facilitate early and appropriate mitigation action. However, the implementation of GMO monitoring at the national and EU-level, specifically for the cultivation of GM plants, proved to be a challenging issue and is subject to ongoing discussions.