Exosomes are cell-derived vesicles that are present in many and perhaps all biological fluids, including blood, urine, and cultured medium of cell cultures. These are small vesicles (30-120 nm) containing nucleic acid and protein, perceived to be carriers of this cargo between diverse locations in the body. Exosomes are either released from the cell when multivesicular bodies fuse with the plasma membrane or they are released directly from the plasma membrane. It is becoming increasingly clear that exosomes have specialized functions and play a key role in, for example, coagulation, intercellular signalling, and waste management. The exosomes are released to extracellular fluids by fusion of these multivesicular bodies with the cell surface, resulting in secretion in bursts. Exosomes are secreted by all types of cells in culture, and also found in abundance in body fluids including blood, saliva, urine, and breast milk.