The assembly and secretion of an extracellular exosome, a membrane-bounded vesicle that is released into the extracellular region by fusion of the limiting endosomal membrane of a multivesicular body with the plasma membrane. [ http://www.ncbi.nlm.nih.gov/pubmed/19442504 http://www.ncbi.nlm.nih.gov/pubmed/25392495 ]