Mitochondria are highly dynamic organelles that continuously change their shape through frequent fusion, fission and movement throughout the cell, and these dynamics are crucial for the life and death of the cells as they have been linked to apoptosis, maintenance of cellular homeostasis, and ultimately to neurologic disorders and metabolic diseases. Over the past decade, a growing number of novel proteins that regulate mitochondrial dynamics have been discovered. Large GTPase family proteins and their regulators control these aspects of mitochondrial dynamics. In this review, we briefly summarize the current knowledge about molecular machineries regulating mitochondrial fusion/fission and the role of mitochondrial dynamics in cell pathophysiology.