Abstract Collective cell movements termed convergent extension (CE) drive the elongation of tissues and organs in essentially all animals. In vertebrates, CE is controlled by the planar cell polarity (PCP) signaling system, and defects in PCP-dependent convergent extension are associated with human neural tube defects and skeletal dysplasias. We feel that the profound lack of information regarding the basic cell biology of CE as it occurs in vertebrate animals in vivo represents the key challenge in the field at this time. Building on our recent successes in advanced imaging and proteomics, this proposal takes a "cell biological" approach, focusing on fundamental cellular machines of cadherin adhesion, actin assembly, and the septin cytoskeleton and how they are deployed to drive PCP-mediated CE.