Every time a hormone is released from a cell, every time a neurotransmitter leaps across a synapse to relay a message from one neuron to another, the cell must undergo exocytosis. This is the process responsible for transporting cellular contents via lipid-encapsulated vesicles to the cell surface membrane and then incorporating or secreting them through membrane fusion. Insights into this cellular cargo transport system won three Americans the Nobel Prize in 2013.