This CMS Workshop Lecture Series (WLS) volume is intended to give a summary of the current state-of-the-art of different spectroscopy and microscopy methods, as presented during a workshop held in conjunction with the EUROCLAY 2015 conference in Edinburgh, UK, on the 5th of July 2015. This workshop was initiated by the NEA Clay Club, The Clay Minerals Society, and the Euroclay conference series. This EUROCLAY 2015 workshop is a continuation of the very successful workshop “Clays under Nano- to Microscopic resolution” which took place from 6^th to the 8^th of September 2011 in Karlsruhe and documents new developments and the progress made over the past four years concerning research in low-permeability, clay-rich, geological formations. The workshop also provided an excellent opportunity for exchange of knowledge with research communities concerned with the safe long-term management of radioactive waste within argillaceous sediments, and with shale gas and oil exploration.