This document provides guidance on best practice for the use of Diffusive Gradient in Thin films (DGT) passive samplers devices in sampling of transitional and coastal waters for water quality monitoring. The methodology1 to be addressed in this guide was developed by the consortium of the European Union’s Interreg MONITOOL Project in order to ensure comparability and reproducibility of the data obtained from each project Partner in different regions. The guide provides practical and detailed information on all the aspects to be considered before the deployment of these devices and the essential steps for their deployment, retrieval and subsequent sample processing for the analysis of trace metals. Although it is not aimed as a standard protocol, these guidelines address the need for a common approach and the intention to promote best practice.