Size and position matter.

The 2013 Nobel Prize in Physiology or Medicine emphasizes the progress made in understanding the molecular mechanisms that underpin the vesicular movement of cargo through the exocytic and endocytic pathways. Attention now focuses on those mechanisms that govern the relative size and position of the many different membrane-bound compartments. These homeostatic mechanisms are discussed in this issue of Nature Reviews Molecular Cell Biology and must be integrated so as to satisfy the needs of the cell and the organism.