This chapter reviewed the various sources of exosomes and their characteristics. Exosomes, which in the context of the proposed chapter are the synonym for extracellular vesicles up to 200 nm, play a pivotal role in cell to cell communication thus leading to the involvement of exosomes in inflammation and cancer development. This brings exosomes to the forefront of promising markers of a sub-clinical stage of the disease, which makes identifying exosome’s source and destination one of the main goals in exosome research. However, due to some biogenesis features and technological difficulties, which are discussed further, identification of a certain exosome’s address, or its specificity for a certain tissue or cell type, becomes a non-trivial task. The chapter covers the following questions: some of the main barriers on the way of testing tissue specificity hypothesis of exosomes, exosomes from synovial fluid and CSF and their features, exosomes from mesenchymal stem cells (MSCs) of different origins, and some membrane and cargo exosomal markers for tissue specificity and the prospect of exosomes as a drug delivery approach
