Discovery of various molecular components regulating dynamics and organization of the mitochondria in cells, together with novel insights into the role of mitochondrial fusion and division in the maintenance of cellular homeostasis, have provided some of the most exciting breakthroughs in the last decade of mitochondrial research. The focus of this review is on the regulation of mitochondrial fusion and division machineries. The newly identified factors associated with mitofusin/OPA1-dependent mitochondrial fusion, and Drp1-dependent mitochondrial division are discussed. Furthermore, the most recent findings on the role of mitochondrial fusion and division in the maintenance of cell function are also reviewed here in some detail.