For nearly 60 years the book “Theory of Dislocations” by John P. Hirth and Jens Lothe has been the authoritative reference on the theory of dislocations. The reputation of the book was that it was not for the feint of heart. Rather it was widely considered to be the authoritative reference to be consulted only after the reader had started with more elementary books on dislocations like “Introduction to Dislocations” by Derek Hull and David J. Bacon or “Elementary Dislocation Theory” by Johannes and Julia R. Weertman. More recently the book by Wei Cai and William D. Nix, “Imperfections in Crystalline Solids” has provided an intermediate introduction to dislocations as a bridge between the more elementary books just cited and the book by Hirth and Lothe, which was written for experienced researchers. Now, with the Third Edition of “Theory of Dislocations,” with Peter M. Anderson as the lead author, the classic book by Hirth and Lothe has been made much more assessible to a wider audience of students and researchers. Without sacrificing any of the rigor found in the first two editions of “Theory of Dislocations,” the Third Edition provides a much more tutorial approach to understanding and appreciating the theory of dislocations.