Book excerpt: In this Atlas I want to share with my fellow clinicians the fascina tion I experienced while discovering the marvels of embryonic development. Why haven't these marvels excited me before? I believe that the use of schemata and drawings or photographs of animal embryos, commonly used in textbooks of embryology, simply did not appeal to me as a clinician. Only actual photo graphs of human embryos can establish the bond necessary for interaction. Just imagine the excitement when you find out how many struc tures you can recognize in a 5-week-old embryo, barely measuring 1 cm in length. But our fascination does not stop here. The pro gression of changes taking place during the next 3 weeks is so rapid that at the time when the embryo measures 3 cm, all structures familiar to us are not only easily recognizable, but also already in their anatomical position. How can we hide our amazement when we realize that such a state of perfection is present in an embryo a bit longer than the distal phalanx of our little finger? At 8 weeks the embryonic period ends and the fetal one starts. Although the shape and the relative size of bones, joints, muscles, nerves, and vessels will undergo changes, the basic elements are all in place. This implies that major malformations must develop during the embryonic period.