Mitochondria are essential organelles for all cell types, especially for neurons, which possess extremely long axons that require the support of mitochondria from cell bodies at great distances. Numerous neurodegenerative diseases are associated with mitochondrial dysfunction, and yet how a neuron maintains a pool of properly sized, functionally sound mitochondria at the correct density throughout large stretches of axons in vivo remains enigmatic. Given that many molecules known for mitochondrial regulation were discovered in non-neuronal cells in an in vitro setting, whether these molecules can translate into in vivo mitochondrial regulation is an open and important question. In this thesis, I utilized the power of Drosophila melanogaster and its extensive toolbox developed by the fruit fly community to study how axonal mitochondria are regulated in vivo.