The book presents mathematical descriptions of physiological processes employed in different approaches to PK/TK modeling. It focuses on emphasizing general principles and concepts, rather than isolated observations. Above all, the book is an effort to blend the pharmaceutical and toxicological aspects of both fields. The systematic compilation of mathematical concepts and methodologies allows readers to decide on relevant concepts and approaches for their research, scientific or regulatory decisions, or for offering advance courses and seminars. This is an invaluable resource for scientists in the pharmaceutical sciences, clinical sciences, and environmental health sciences, as well as those involved in drug discovery and development.