Transmission of information from mast cells to neighboring or distant cells must be established continuously in order to ensure homeostasis or to initiate immune and inflammatory responses. Owing to their strategic location in peripheral tissues and their prompt response to various stimuli, mast cells can be considered as the cell prototype to fulfill such a sentinel function. There are several ways for mast cells to communicate with other cells including cell-cell interactions via membrane-associated receptors, cytokines and other soluble mediators, and a newly described messenger which consists of membrane vesicles called exosomes carrying a number of immunoregulatory molecules.