Eukaryotic and prokaryotic cells produce minute (40-1000 nm) membrane vesicles that are released into the local environment. These extracellular vesicles (EVs), including exosomes and microvesicles, contain a multi-molecular cargo of proteins, nucleic acids, lipids and metabolites. Together with the number of EVs, this “EVome” reflects the state of the organism and is subject to change upon environmental cues and the activation state of the cell. EVs may thus target recipient cells by e.g. the transfer of genomic material, or influence them by signaling lipids in the EV membrane. EVs have already been shown to function in various roles of cell-cell communication, in processes ranging from the regulation of immune responses – both good and bad – to cancer metastasis. The novel mechanism of cell signaling via EVs is a hot topic of contemporary cell biology. At the same time, there is a fast increasing interest in the use of EVs in diagnostics (liquid biopsies), therapeutics, and in drug delivery. The composition and quantity of EVs changes in many diseases, and is actively studied in cancer, opening possibilities for the use of EVs as early diagnostic or prognostic indicators. Furthermore, EVs may carry much of the therapeutic potential of stem cells and could be utilized in the treatment of complex diseases.