The ICES Working Group on Mixed Fisheries Methodology (WGMIXFISH-METHODS) meet to progress work on the improvement and development of the mixed fisheries advice. In this report the group provides a summary of the work completed in 2020. Work continued on the full documentation of the mixed fisheries advice production process, including workflows, code repositories, stock annexes and associated documentation for all advice regions. A review was completed of the new data call and associated quality control procedures to identify possible areas of improvements. Working group participants responded to the outcomes and issues encountered during WGMIXFISH-Advice 2019 for Celtic Sea, Iberian Waters, and North Sea. A full list of issues and solutions were collated and discussed during the meeting. Additionally, work continued on the development of mixed fisheries advice for three new advice regions: Bay of Biscay, Irish Sea, and Kattegat. The working group responded to the outcomes of the Mixed Fisheries Scoping Meeting (WKMIXFISH), identifying timelines and requirements to meet the growing needs for mixed fisheries advice. To support these growing needs the group members presented and discussed new techniques in the field of mixed fisheries.