Mitochondria play critical roles in all cell types. They are involved in processes such as calcium storage and signaling, cell proliferation, apoptosis, steroid synthesis, immunity, energy balance, and heat production. Inherent to these vital functions, mitochondria represent frequent targets for toxicity and disease. A plethora of toxicants are indeed known to affect mitochondria. Furthermore, >200 clinical pathologies have been associated with impairment of mitochondrial functionality, including cancer, inflammatory disorders, neurodegenerative diseases, and diabetes. Both structural defects and functional deterioration may underlie mitochondrial toxicity, and as such form key events in various adverse outcome pathways (AOPs). Not surprisingly, mitochondrial toxicity is increasingly gaining attention by toxicologists and, therefore, was the central theme of this expert roundtable discussion.