According to Directive 2001/18/EC commercial cultivation of genetically modified plants (GMPs) have to be monitored. The aim of the monitoring is to identify potential adverse effects of the GMPs and their use on human health and the environment. There are few concepts showing how GMP monitoring may be implemented. This article indicates monitoring requirements with a focus on environmental issues. GMP monitoring has to be appropriate to detect direct and indirect, immediate and long-term as well as unforeseen effects. For choosing suitable monitoring indicators and methods, we propose a case-by-case approach, which is hypothesis-driven and related to specified protection targets. We present criteria for selecting suitable monitoring sites and demonstrate possibilities to integrate GMP monitoring with existing environmental monitoring programmes. To ensure comparability, interpretability and quality of GMP monitoring data a harmonisation on both national and international
level is proposed.