The fate and bioavailability of trace elements in the environment are strongly influenced by their chemical speciation and interactions with mineral(oid) particles in soils and aquatic systems. The most chemically reactive minerals and mineraloids in the environment are in the colloidal to nanoparticle size range, resulting in large specific surface areas and high densities of reactive surface sites. Chemical processes involving mineral particles include, for example, sorption/desorption, (co)precipitation/dissolution, and electron transfer (redox) reactions. A combination of analytical, microscopic, and theoretical advances has led to significant progress in our understanding of mineral surface reactions, mineral phase transformations, incorporation of trace elements into crystal structures, mineral − microbe and natural organic matter − mineral interactions, and the influence of such processes on trace element cycling. This lecture will provide an overview of the role of mineral(oid) particles in trace element speciation and cycling in the environment, illustrated by selected research results. Special focus will be given to our current research on redox-driven mineral transformations and their implications for trace element behaviour in soils and sediments.