Abstract: The 12 th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere took place in Kennewick, Washington State, USA on 20-25 September 2009.This time, the conference venue was located close to a historical site with regard to the origins of nuclear technology -the Hanford site.Certainly a highlight of the conference was the opportunity to visit the B-reactor, the first large scale nuclear reactor ever built, which started operation in 1944.Roy E. Gephart (PNNL, USA) introduced at the conference opening the history and present state of the Hanford site in an excellent presentation.The behavior of actinides and fission products released to the environment at the site was then subject of a special session, where various contributions focused on geochemistry aspects down to the molecular speciation of individual radionuclides.The session was introduced by an impressive keynote lecture given by John Zachara (PNNL, USA) on the interpretation and modeling of radionuclide transport under complex hydrogeological conditions based on microscopic and spectroscopic investigations.