If the effects of immigration are mainly in the future, the discussion of them must be, for the most part, theoretical. It is a discussion of something which is going to happen, or which is likely to happen, not of something that has happened. This gives it an element of uncertainty and speculation which is not wholly desirable in a scientific study. Yet this is the phase of the subject which is by far the most interesting and important to the average American citizen who wants to know how this great sociological phenomenon is going to affect him, and his country, and his relatives and friends. His attitude toward the question will depend upon what he believes these effects will be. If it appears to him that immigration will benefit himself, his country, the immigrants, or humanity in general, he will favor it; if his belief is to the contrary, his attitude will be one of opposition. Since there is no certainty as to what the effects will be, the arguments about immigration are largely composed of attempts to prove that certain effects have transpired, or to demonstrate that they will transpire. As a consequence, it comes about that the discussion of the effects of immigration practically resolves itself into a consideration of the arguments for and against immigration, and it will be so treated, for the most part, in the following chapters. There are three classes of effects of immigration which may be clearly distinguished, and which will interest different persons in different degrees. These are the effects upon the United States, the effects upon the countries of source, and the effects upon the immigrants themselves. The second and third of these interest the American citizen only as he is open to broad humanitarian considerations; the first touches him directly, and may have an intimate bearing on his personal and selfish interests and pursuits. If a seemingly disproportionate space is given in this volume to effects in general, and effects upon the United States in particular, it is because this is the vital and imperative part of the whole subject to the people of this nation.