The need for harmonized monitoring protocols for marine microplastic has been discussed for many years, but how to reach this goal has not been agreed upon. Important questions addressed when microplastics are monitored are: how to carry out field sampling, how to eliminate other particulate matter from a sample without harming the microplastics, and how to accurately identify the particles, while also preventing and assessing potential sample contamination at each step from sampling to analyses. In the project HARMIC, Nordic scientist with long term experience in microplastic research, applied and evaluated different methods for sampling and sample preparation relevant for the establishment of common guidelines. The outcomes of the studies are discussed from a monitoring perspective, including aspects of quality assurance and quality control.