Mitochondria are highly dynamic organelles that continuously divide and fuse. A balance between these two activities is essential for regulating mitochondrial size and number. In this seminar, I will discuss Mitochondrial Safeguard (MitoSafe), a new defense mechanism that inhibits mitochondrial fusion when mitochondria become excessively large. Additionally, I will explore an unexpected role for a mitochondrial division GTPase, Drp1, in forming endoplasmic reticulum tubules that interact with mitochondria.