The structure of mitochondria is highly dynamic. Mitochondrial shape is cell-type specific and can be modified to meet changing requirements in energy production, calcium homeostasis, lipid biogenesis, fatty acid synthesis and other mitochondrial activities. This is achieved by modulating the dynamic properties of mitochondria including fusion, division, movement and positional tethering. It has become increasingly evident that mitochondrial dynamics also play an intimate role in several cellular signaling pathways and as such, many mechanisms have evolved to modulate mitochondrial structure. These regulatory mechanisms turn out to be important for modulation of mitochondrial-specific processes as well as cell, tissue and organism responses to developmental or environmental cues.