This COMET workshop comprised of three events in July 2015. These were (i) A special session at the 13th International Conference on the Biogeochemistry of Trace Elements (ICOBTE) held at the Fukuoka International Congress Centre on 12th – 16th July 2015. The Symposium was on “Understanding and mitigating the environmental behaviour of radiocaesium after the Fukushima accident”. There were 73 presentations, including 25 posters, from 9 countries. (ii) an associated excursion on 17th July 2015 to the region affected by the Fukushima accident, and (iii) the COMET Fukushima Workshop at Iizaka, Fukushima, on the 18th – 19th July 2015. The workshop, organised by the Institute for Environmental Radioactivity at Fukushima University, had 42 participants from 6 countries. The speakers covered a wide range of topics and summarised current key findings and issues.

COMET Deliverable 5.4 describes each of the three activities, summarises their content and considers the main messages for both Japan and the wider international community.