Metals are prevalent in the environment. They are derived from both natural and anthropogenic sources. Certain metals are essential for plant growth and for animal and human health. However, if present in excessive concentrations they become toxic. Metals undergo an array of biogeochemical processes at reactive natural surfaces, including surfaces of clay minerals, metal oxides and oxyhydroxides, humic substances, plant roots, and microbes. These processes control the solubility, mobility, bioavailability, and toxicity of metals in the environment. The use of advanced analytical techniques has furthered our understanding of the reactivity and mobility of metals in the near-surface environment.