The mitochondria are the energy-generating organelles in the cytoplasm of the cell. They also serve as signaling organelles that coordinate complex cellular functions. Mitochondria are highly dynamic and undergo fusion and fission processes continuously, which is crucial for the maintenance of mitochondrial homeostasis and the balance of mitochondrial turnover. Although most of the evolutionarily conserved core components of the mitochondrial fusion and fission machineries have been identified in the past decade, the mechanistic insights into their molecular functions remain to be investigated. Mitochondrial fusion and fission (collectively termed mitochondrial dynamics) takes part in cellular quality control system and play a key role in the development of the cell, tissue and organism. Dysfunctions of mitochondrial dynamics are implicated in various inherited and age-related neurodegenerative diseases. Thus, the research in the relationship between mitochondrial biology and diseases will remain an exciting field in the coming years.