The skeletal dysplasias are a large heterogeneous group of genetic conditions characterized by abnormal shape, growth, or integrity of bones. Often, there may be prominent features associated with other organ systems as part of a more encompassing skeletal malformation syndrome. Tremendous advances have been made in the clinical and molecular delineation of these conditions over the past 20–30 years. We have progressed from initial broad clinical classifications of these conditions in the first two-thirds of this century, to extensive delineation based on radiographic features in the 1970s and 1980s, to the present reconsideration and grouping of these conditions according to their molecular pathogenesis. This has in part been spurred on by advances in the understanding of the developmental pathways which govern skeletal development, as well as by the human genome sequencing effort, which has provided a plethora of positional candidate genes for many of these conditions. The pathogenetic correlations derived from such studies are often based on parallels between the human phenotype and mouse models of the human condition, and have sometimes revealed novel developmental functions.