Mitochondria constitute a dynamic network whose morphology is conditioned by an equilibrium between fission and fusion events of their membranes. These processes are essential to shape the ultra-structure of the mitochondrial compartment and are thus also crucial for all mitochondrial functions. Consequently, defects in mitochondrial fusion and fission are associated with numerous pathologies. To modulate their membrane dynamics, mitochondria developed an evolutionary conserved strategy that involves large GTPases of the Dynamin-Related Proteins (DRPs) family. While the mechanism by which DRPs promote membrane fission is well understood, how they can also promote mixing of lipid bilayers remains unclear. MITOFUSION thus aims at dissecting how DRPs promote attachment and fusion of mitochondrial outer membranes. For this purpose, a multidisciplinary combination of approaches allying cell and structural biology, biophysics, biochemistry and bio-informatics methods will be employed.