  Branching morphogenesis generates epithelial trees which facilitate gas
exchange, filtering, as well as secretion processes with their large surface to
volume ratio. In this review, we focus on the developmental mechanisms that
control the early stages of lung branching morphogenesis. Lung branching
morphogenesis involves the stereotypic, recurrent definition of new branch
points, subsequent epithelial budding, and lung tube elongation. We discuss
current models and experimental evidence for each of these steps. Finally, we
discuss the role of the mesenchyme in determining the organ-specific shape.
