Exosomes are nanosized membrane vesicles released by fusion of an organelle of 
the endocytic pathway, the multivesicular body, with the plasma membrane. This 
process was discovered more than 30 years ago, and during these years, exosomes 
have gone from being considered as cellular waste disposal to mediate a novel 
mechanism of cell-to-cell communication. The exponential interest in exosomes 
experienced during recent years is due to their important roles in health and 
disease and to their potential clinical application in therapy and diagnosis. 
However, important aspects of the biology of exosomes remain unknown. To explore 
the use of exosomes in the clinic, it is essential that the basic molecular 
mechanisms behind the transport and function of these vesicles are better 
understood. We have here summarized what is presently known about how exosomes 
are formed and released by cells. Moreover, other cellular processes related to 
exosome biogenesis and release, such as autophagy and lysosomal exocytosis are 
presented. Finally, methodological aspects related to exosome release studies 
are discussed.