Mitochondria act at the interface of numerous processes critical for cellular function and organismal health. Recent years have seen a growing appreciation for the diverse roles that mitochondria play not only in energy production and metabolism, but also in maintenance of redox balance, regulation of gene expression, ion homeostasis, and control of cell fate. Mitochondrial maintenance is critical for proper function of cells and tissues, and mitochondrial dysfunction underlies numerous disease processes ranging from severe childhood mitochondrial disorders, to heart disease, neurodegenerative disorders, cancer, and aging itself.