Isotopic analysis of the sedimentary record across major extinction horizons plays a major role in interpretion of the causal mechanisms and environmental effects. E.g. variations in 187Os/188Os, 143Nd/144Nd and 53Cr/52Cr ratios across the K/T boundary identify the type of impacting bolide and the impacted target rocks. 87Sr/86Sr ratios and stable isotope values (δ13C, δ18O, δ15N, δ2H) are used for interpretation of environmental and oceanographic changes. This session aims to debate and discuss the role of isotopic systems in the unravelling of such major upheavals in the geological record.