An Outline of Developmental Physiology was first published in the Dutch language in 1948, while the first English edition appeared in 1954. It was meant in the first place for readers who, though interested in its subject and having some general knowledge of science, were not acquainted with more than the first elements of biology. This new edition has been brought up to date by taking into account the literature up to about the middle of 1963. The book opens with a discussion of the fusion of sperm and egg. This is followed by separate chapters that explain the series of processes that transform the initially fairly homogeneous structure of the egg into a system with a considerable degree of spatial multiplicity. This book may be used as a preliminary introduction into the field in undergraduate classes. A list of references has been added in the interest of those who might want to refer to the original publications on some special problem. Moreover, a glossary of scientific terms has been included for the benefit of those readers who are not professional biologists.