The evolution to multicellular organisms determined the appearance of more sophisticated and specialized systems for the different physiologies like integumentary, respiration, digestion, excretion, circulatory, reproduction, skeletal and the nervous system. In the line of chordate evolution, advent of tetrapods have triggered the events leading to only partial dependence on water for physiological activities. The inconstant environment in which animals lives largely determine and guides the way animal physiology evolves. This directs the anatomical and morphological changes in the organism that translates into varied and diverse physiological process. This book describes the transition of life from aquatic to terrestrial habitat that brings about changes in feeding habit and subsequent anatomical and morphological changes in the digestive tract. Similar transition also guides modifications in urino-genital system due to demands of removing ammonia/urea or uric acid as excretory waste. The author of this book further explores the evolution of tetrapods as one major event in the evolutionary history of chordates in addition to adaptive radiation. This has transformed the locomotion from Fins' to Feet'. Demands of terrestrial life also means metabolism and energy requirements has to be met for which circulatory system was modified to incorporate more chambers and double circulation for warm bloodedness and increased metabolism to meet the energy requirements of life on land. Subsequently, as explored in the book, different organ systems underwent modification in organization to work together the best physiological adaptations to sustain life on earth.