Learning about rocks can give much pleasure to anyone interested in Earth and its development. I hope that readers of this book will share my enthusiasm for examining rocks with the microscope. I planned the book to be an introductory review of the main processes responsible for the microstructures of Earth rocks. However, I soon realized that if I did that, the book would be a collection of half-truths, with little scientific value. Though many rock microstructures are understood fairly well, the interpretation of many others involves considerable controversy, and new ideas are being published all the time. So, I have felt compelled to mention problems of interpretation and to present alternative views, where appropriate. Thus, the book has evolved into (1) a basic explanation of the main processes, (2) an introduction to more complex issues of interpretation and especially to the relevant literature, and (3) an outline of modern approaches and techniques, in order to emphasize the ongoing, dynamic nature of the study of rock microstructure. Because complicated problems cannot be discussed in detail in a book of this kind, I have tried to provide a sufficient number of references to enable the reader to delve more deeply.