Mitochondria are double membrane-bounded organelles that perform a myriad of diverse and essential functions in cells.  These functions are dependent on the collective intracellular behavior of the organelle. We have characterized key features of mitochondrial behaviors.  Our work has addressed the physiological functions and mechanisms of mitochondrial division and fusion, which are important determinants of overall mitochondrial shape and distribution.  We have uncovered contact sites that intimately link mitochondria with the ER and determined their roles in mitochondrial positioning, dynamics and mtDNA transmission.  We have also addressed the fundamental question of how mitochondrial membranes are sub-compartmentalized to reveal how the complex internal architecture of the organelle is generated.  Our current focus is to determine how mitochondrial behaviors are integrated with one another and physiologically regulated within cells and organisms.