In the years after the war the problem of population and especially the birth-rate movements excited general interest in all countries. In the Netherlands also all kinds ot scientific men occupied themselves with this subject; not only economists, sociologists and theologians but also medical men studied the population problem in all its various aspects. It has appeared that it is only possible to obtain a complete analysis of the population problem by making a careful scientific investigation of every part of it. Evidently this was also the author’s conception of the problem. By examining 25000 families he submitted the birth-rate movement of a large town to a scientific investigation. Neither political nor religious or other than scientific motives prompted him in undertaking this work; the examination was begun and ended quite objectively which lends this book its value. For only an objective examination of s~tch a complex phe- nomenon like the birth-rate movement is of importance for science. The examination was inspired by the working program of the I nterna- tional Union for the scientific Investigation of Population Problems. It produces surprising results and shows in figures how natality presented itself in a metropolis like Rotterdam during the last fifty years. It is to be hoped that this study may be followed by many similar in- vestigations, also for the country.