Mitochondria couple cellular metabolic state with Ca²⁺ transport processes. They therefore control not only their own intra-organelle [Ca²⁺], but they also influence the entire cellular network of cellular Ca²⁺ signalling, including the endoplasmic reticulum (ER), the plasma membrane and the nucleus. Through the detailed study of mitochondrial roles in Ca²⁺ signalling has emerged a remarkable picture of inter-organelle communication. The talk will give an overview of this picture and focus on data showing (i) preferential Ca²⁺ transfer from the ER to the mitochondrial matrix through a macromolecular complex associated with the both mitochondrial and ER membranes (ii) Ca²⁺ dependent regulation of mitochondrial movements and cellular distribution through the mitochondrial Rho GTPase Miro.