Microplastics are emerging pollutants in aquatic and terrestrial environments. In the last years, several case studies and reviews have been published about microplastics in freshwater and marine environments. However, no standardized methods are available for sampling and sample preparation. Based on literature research, this review presents different techniques and methods for sampling as well as the preparation of microplastic samples from water, sediment and biota of freshwater and marine environments. Several methods are used for sampling and sample preparation (e.g., organic digestion and density separation) which influence the interpretation of results and hamper their comparability. The results clearly show that the basis for the interpretation of the results of microplastic monitoring is the consistency of a sampling strategy. Until standardization and harmonization both for sampling and sample preparation is implemented, further research about processing of samples and analysis techniques is necessary. •Comparison of different sampling methods for water, sediment and biota.•Sample preparation with organic digestion and density separation.•Standardization and harmonization of sampling and sample preparation methods is needed.