The primary purpose of this new book is just what the title implies; namely, to provide the student with information requisite for an understanding of rocks as seen in thin section. To this end, the text is subdivided into live major parts: The first of those (37 pages) deals in a brief but adequate manner with the methods of optical mineralogy. As the author points out, this section is not intended to replace standard texts, but rather to serve as a review, in which capacity it should prove very useful.