The subject of the following work may be expressed in three questions: What is evolution? Is it true? What then? Surely, there are no questions of the day more burning than these. Much has been written on each of them, addressed to different classes of minds: some to the scientific, some to the popular, and some to the religious and theological; but nothing has yet appeared which covers the whole ground and connects the different parts together. Much, very much has been written, especially on the nature and the evidences of evolution, but the literature is so voluminous, much of it so fragmentary, and most of it so technical, that even very intelligent persons have still very vague ideas on the subject. I have attempted to give (1) a very concise account of what we mean by evolution, (2) an outline of the evidences of its truth drawn from many different sources, and (3) its relation to fundamental religious beliefs. I have determined, above all, to make a book so small that it may be read through without much expense of time and patience. But the subject is so large that in order to do so it was necessary to sacrifice all but what was most essential, and to forego all redundancy (the bane of so-called popular science) even at the risk of baldness and obscurity.