Extracellular vesicles (EVs) are increasingly being recognised as players in intercellular communication within the human body. EVs are nano-sized vesicles that are secreted by virtually all cells, primarily arising from either the plasma membrane or the endocytic system. They contain a wide range of proteins and nucleic acids in their lumen, as well as cell surface proteins on their exterior. The proteins and nucleic acids within are the 'cargo' that EVs deliver into the cytosol of recipient cells to elicit a response or phenotypic change. For delivery to occur, the cargo needs to cross two lipid bilayers; one that makes up the vesicle itself, and the other of the recipient cell. Exactly how this process works is a topic that is poorly understood, despite being pivotal for their function. Furthermore, extracellular vesicles have therapeutic potential as drug delivery vehicles. Therefore, understanding their delivery mechanism and harnessing its action for drug delivery is of great importance. This chapter will focus on the proposed mechanisms for cargo delivery and discuss existing evidence for cargo delivery from EVs into the cytosol of recipient cells.