Vascular networks are formed and maintained through a multitude of angiogenic processes,
such as sprouting, anastomosis and pruning. Only recently has it become possible to study
the behavior of the endothelial cells that contribute to these networks at a single-cell level in
vivo. This Review summarizes what is known about endothelial cell behavior during
developmental angiogenesis, focusing on the morphogenetic changes that these cells
undergo.