In the following pages I have sought to present an approach to that common humanity which is to be found in the development of the individual as he moves through the age-grades of the life-cycle. Life itself is neither a continuous process nor a static set of conditions: it is a stage-process through which the developing individual moves, like a figure in the separate frames of a motion picture film. I have sought to describe the essence of these frames and in this way to characterize the individual for what he is: a member of a species. To this end I have had to neglect the differences in human life and to concentrate on what is similar, though no doubt the differences are as significant as the similarities. To have concentrated on the differences, however, would have been to write as many biographies as there are individuals. We can learn something about each and every individual from a study of the typical individual, and that is what I have sought to undertake here.