This book describes the physical microenvironment of living organisms. It presents a simplified discussion of heat and mass transfer models and applies them to exchange processes between organisms and their surroundings. Emphasis is placed on teaching the student how to calculate actual transfer rates, rather than just studying the principles involved. Numerous examples are provided to illustrate many of the principles, and problems are included at the end of each chapter to help the student develop skills in using the equations and to gain an understanding of modern environmental biophysics. The book is an engineering approach to environmental biology.