The cells continuously secrete a large number of different types of microvesicles including macro-and micro-molecules into the extracellular fluids. One of them are exosomes, which are nano-sized vesicles capable of transferring the DNAs, microRNAs, non-coding RNAs and lipids with or without direct cell to cell contact, so representing the novel way of intracellular communication. In this review, we tried to summarize the exosomal structure, composition, formation, and isolation. We also discussed their active role in pathogenesis. The potential use of exosomes for diagnostic and therapeutic purposes in various diseases is also discussed. Exosomes are perceived to be used as carriers between different locations of body. Exosomes are secreted by all types of cells and are also found abundantly in the body fluids such as: saliva, blood, urine and breast milk. The major role of exosomes is to carry the information by delivering various effectors or signaling molecules between specific cells. This review summarizes current knowledge about the exosomes, their functions, biological and therapeutic use as well as emerging exosomes based therapies that could not be applied before.