Trace elements, such as the Y+REE, actinides, LIL, and HFSE, are one means by which fluid movement in the Earth’s crust and upper mantle can be surveyed. The partitioning of trace elements between fluids and the various minerals, both accessory and otherwise, that host them can give information concerning the chemistry of the fluids involved as well as the mechanics by which the host mineral chemically reacts with these fluids. The goal of this session is to explore current research on trace element mobility with regard to their role during local and regional metamorphism; their behavior during the dehydration and subsequent metamorphism of subducting oceanic crust; as well as their behavior during igneous processes such as spreading oceanic ridge centers or emplacement of granitoid batholiths.