Human genealogy is one of the oldest manifestations of man's intellectual activity, but until recently it has been subservient to sentimental purposes, or pursued from historical or legal motives. Biology has had no place in it. Genealogy, however, has not altogether escaped the re-examination which all sciences received after the Darwinian movement revolutionized modern thought. Numerous ways have been pointed out in which it could be brought into line with the new way of looking at man and his world. The field of genealogy has already been invaded at many points by biologists, seeking the furtherance of their own aims. It will be worth while to discuss briefly the relations between the conventional genealogy and eugenics. It may be that genealogy could become an even more valuable branch of human knowledge than it now is, if it were more closely aligned with biology. In order to test this possibility, one must inquire: (1) What is genealogy? (2) What does it now attempt to do? (3) What faults, from the eugenist's standpoint, seem to exist in present genealogical methods? (4) What additions should be made to the present methods? (5) What can be expected of it, after it is revised in accordance with the ideas of the eugenist? The answer to the first question, "What is genealogy?" may be brief. Genealogy may be envisaged from several points. It serves history. It has a legal function, which is of more consequence abroad than in America. It has social significance, in bolstering family pride and creating a feeling of family solidarity--this is perhaps its chief office in the United States. It has, or can have, biological significance, and this in two ways: either in relation to pure science or applied science. In connection with pure science, its function is to furnish means for getting knowledge of the laws of heredity. In application, its function is to furnish a knowledge of the inherited characters of any given individual, in order to make it possible for the individual to find his place in the world and, in particular, to marry wisely. It is obvious that the use of genealogy in the applied science of eugenics is dependent on previous research by geneticists; for marriage matings which take account of heredity can not be made unless the mode of inheritance of human traits has previously been discovered. The historical, social, legal and other aspects of genealogy do not concern the present discussion. We shall discuss only the biological aspect; not only because it alone is germane to the present book, but because we consider it to have by far the greatest true value, accepting the criterion of value as that which increases the welfare of mankind. By this criterion, the historical, legal and social aspects of genealogy will be seen, with a little reflection, to be of secondary importance to its biological aspect.