Longitudinal growth of the skeleton is a result of endochondral ossification that occurs at the growth plate. Through a sequential process of cell proliferation, extracellular matrix synthesis, cellular hypertrophy, matrix mineralization, vascular invasion, and eventually apoptosis, the cartilage model is continually replaced by bone as length increases. The regulation of longitudinal growth at the growth plate occurs generally through the intimate interaction of circulating systemic hormones and locally produced peptide growth factors, the net result of which is to trigger changes in gene expression by growth plate chondrocytes. This review highlights recent advances in genetics and cell biology that are illuminating the important regulatory mechanisms governing the structure and biology of the growth plate, and provides selected examples of how studies of human mutations have yielded a wealth of new knowledge regarding the normal biology and pathophysiology of growth plate cartilage. Birth Defects Research (Part C) 69:123–143, 2003. © 2003 Wiley-Liss, Inc.