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The development and function of mammalian cells, like other multicellular animals, requires cell to cell interactions, which are carried out directly via cellular junctions or indirectly by secretion of secretory molecules such as hormones. During the last two decades, exosomes have been introduced as the third mechanism for cellular interactions. Exosomes are small vesicles with membranes and 30 to 100 nm in size that exist in blood, urine, saliva, semen, and serum. Exosomes play an important role in a variety of biological processes such as immune response and inflammation, pregnancy, tissue generalization, blood coagulation, and angiogenesis. Exosomes are also involved in pathologic process such as neurological disorders, cancer, infectious diseases, and cardiovascular diseases. Because of their small size, exosomes are able to cross the cell membrane and protect the proteins from degradation. They also have the potential of transferring different compounds into the cell. Due to their receiver specificity, lack of inducing immune system, and more importantly having the capacity to be engineered as drug carriers, exosomes have been introduced as new agents for the transfer of genetic material and disease treatment.