Oxidative stress is arguably the most common mechanism in the toxicology of environmental agents, unifying the action of broad classes of physichochemically disparate environmental pollutants, including oxidant gases, organic compounds, particulate surfaces, and metal ions. As advances in redox biology identify previously unrecognized targets for disruption by exposure to xenobiotics, redox toxicology has emerged as a new field of investigation. Environmental contaminants can induce oxidative stress on cells through mechanisms that are direct, indirect or involve the disruption of metabolic or bioenergetic processes that are regulated by thiol redox switches. Live-cell imaging has proven to be a powerful approach to the study of environmental oxidative stress. Cells are equipped with multiple complementary energy-dependent systems for maintaining redox homeostasis in the face of environmental oxidative stress.