The article by Kowal, Tkach, and Théry provides an in-depth review of the biogenesis and secretion of exosomes, a type of extracellular vesicle (EV) that has gained significant attention in recent years. Exosomes are membrane-enclosed vesicles formed within eukaryotic cells in multivesicular compartments (MVBs) and are secreted when these compartments fuse with the plasma membrane (PM). The formation of exosomes involves the action of several molecular machineries, including the endosomal sorting complex required for transport (ESCRT) machinery, lipids such as ceramide, and tetraspanins. Different families of molecules, such as RAB proteins, are involved in the targeting and fusion of MVBs with the PM, leading to exosome secretion. The review highlights the heterogeneity of exosomes, with different subtypes co-secreted and potentially having distinct functions. It also discusses the challenges in separating these subtypes and the need for improved purification methods. The authors emphasize the importance of understanding the cell biology of exosome formation and secretion to address the physiological relevance of exosome release in vivo.The article by Kowal, Tkach, and Théry provides an in-depth review of the biogenesis and secretion of exosomes, a type of extracellular vesicle (EV) that has gained significant attention in recent years. Exosomes are membrane-enclosed vesicles formed within eukaryotic cells in multivesicular compartments (MVBs) and are secreted when these compartments fuse with the plasma membrane (PM). The formation of exosomes involves the action of several molecular machineries, including the endosomal sorting complex required for transport (ESCRT) machinery, lipids such as ceramide, and tetraspanins. Different families of molecules, such as RAB proteins, are involved in the targeting and fusion of MVBs with the PM, leading to exosome secretion. The review highlights the heterogeneity of exosomes, with different subtypes co-secreted and potentially having distinct functions. It also discusses the challenges in separating these subtypes and the need for improved purification methods. The authors emphasize the importance of understanding the cell biology of exosome formation and secretion to address the physiological relevance of exosome release in vivo.