Marine planning in the UK and Ireland is committed to applying an ecosystem-based approach. A total of seven marine plans from England, Scotland, Wales and Ireland were compared and assessed, using a checklist approach, to evaluate the extent to which they could be considered ecosystem-based. This study is the first to comprehensively assess existing UK and Irish marine plans and processes against each other, according to a consistent set of criteria. The study offers an early indication about the effectiveness and ambition of ecosystem-based marine planning across the UK and Ireland, highlighting areas of positive progress as well as areas of potential improvement. The study also assesses the usefulness of the checklist approach in this context and makes recommendations on how it could be improved.