Improving our understanding of diaphragmatic development is essential to making progress in defining the pathogenesis and genetic etiologies of congenital diaphragmatic defects in humans. As mouse genetic technology has given us new tools to manipulate and observe development, a number of mouse models have recently emerged that provide valuable insight to this field. In this article, we review our current understanding of diaphragmatic embryogenesis including the origin of diaphragmatic tissue. We use rodent models to review the muscularization of the diaphragm and review selected genetic models of abnormal muscularization. We also review models of posterior diaphragmatic defects and discuss evidence for the pleuroperitoneal fold (PPF) tissue contributing to the diaphragm. Finally, we discuss models of anterior and central hernias. It may be simplistic to subdivide this review based on anatomic regions of the diaphragm, as evidence is emerging that defects in different regions of the diaphragm in humans and in mice may be etiologically related. However, at this time we do not have enough knowledge to make more mechanistic or genetic classifications though with time, genetic progress in the field of diaphragm development will allow us to do this. © 2007 Wiley-Liss, Inc.