This book presents a brief history of papermaking followed by comments regarding wood as a source of fibers, including its chemical and anatomical characteristics and the influence of these aspects on the quality of the pulp produced. In addition, the author describes the effects of the pulping process, mainly a chemical process, on pulp quality and how these wood characteristics influence both the refining process as the quality of the final paper. The book further provides a broad discussion, based on experimental results, on the contribution of the main operating refining variables and the main strategies that can be used industrially to optimize the operating results. From this evaluation, the parameter that complements the specific edge load theory is identified. This parameter is related to the retention time of the fiber flocs inside the refiner.