As a common concept ‘bone age’ is felt to be an expression of the biological maturity of a child. Inferring from bone maturity, the clinician can contemplate diagnostic considerations and evaluate height prediction. A radiogram of the hand and wrist may provide additional information that is not being evaluated by reading of a ‘bone age’. Although it reveals only calcified elements it provides a glimpse into a whole variety of processes in bone and cartilage growth, differentiation and calcification which, in turn, are regulated by control mechanisms. Thyroid hormones, sex steroids, calcium regulating hormones are but a few of these control mechanisms, and their effect may become evident when radiograms are carefully examined. This book illustrates how to interpret the biological mechanisms of growth from hand and wrist x-rays reviewing at the same time the anatomical and histological maturation of long bones and cuboid bones. It summarizes the endocrine regulation of these maturational processes and attempts to uncover endocrine functions and malfunctions as they unfold in the radiogram. The presently used methods of skeletal maturity assessment are outlined and reiterated, while some doubts about the entire paradigm and its uncertainties are to be raised and considered. This book is an indispensable aid enabling endocrinologists, radiologists and pediatricians to understand skeletal maturity in a more meaningful way.