Mitochondria are tubular, highly dynamic organelles that continuously fuse and divide in a regulated manner. A balance of fusion and division controls mitochondrial morphol-ogy; imbalanced dynamics leads to altered morphology, which is associated with a variety of pathological conditions. When fusion is decreased, mitochondria fragment into small, spherical mitochondria that are often characterized by swollen cristae and impaired respiratory functions. When division is inhibited, tubular mitochondria fuse, generating elongated mitochondrial tubules with increased connectivity. In some neurons, however, decreased division leads to enlarged, spherical mitochondria.Highlighting the importance of mitochondrial fusion and division in human health and disease, mutations in mitochondrial dynamics components have recently been linked to several neurodevelopmental and neurodegenerative diseases, including a birth defect with multiple neurological disorders (Drp1), Parkinson’s disease (Parkin and Pink1), autosomal dominant optic atrophy type 1 (Opa1), and Charcot-Marie-Tooth neuropathies (Mfn2 and GDAP1). In addition, although Alzheimer’s and Huntington’s diseases are not associated with such mutations, they do show altered activity and abundance of mitochondrial dynamics components.