Mitochondria fuse and divide in response to cell demands and environment. Alterations in mitochondrial dynamics underlie various human diseases, including cancer and neurologic and cardiovascular diseases. Defining the alterations may identify potential therapeutic targets. Mitochondria are mobile organelles that exist in dynamic networks. They continuously join by the process of fusion and divide by the process of fission. Mitochondria are derived from eubacterial endosymbionts that are capable of aerobic respiration; this finding was proposed independently by Merezhkovsky in 1905 and by Margulis in 1967.(1) First described as bioblasts by Altmann in 1890, it was Benda's 1898 observation of their heterogeneous morphologic features, sometimes ball-shaped and other times linear, that inspired the name mitochondrion, from the Greek words mitos (meaning thread) and chondrion (meaning granule).(2) Lewis and Lewis's 1914 observations established the field of mitochondrial ...