Life on Earth is adapted to our planet's 24-hour rotation and orbital revolution around the sun. The circadian clock is an organism's natural timing device. It establishes a link between the organism and its external environment to drive rhythms in feeding, activity and rest, body temperature, and hormones, and it ranges from the level of the cell to the whole organism and from bacteria to mammals. The biological clock has emerged as a potent regulator of human physiology, and it orchestrates cellular trafficking to achieve whole-body metabolic synchronization. A temporary mismatch between this internal biological clock and our external environment could increase the risk for various diseases such as cardiovascular diseases, diabetes, obesity, infertility, neurological disorders, and cancer. This book is comprised of twenty chapters written by experienced and passionate academics and professionals and will be a valuable source of information for scientists and clinicians. Collectively, this book has provided a comprehensive account of our current knowledge about emerging insights into the circadian rhythm in physiology and diseases. It will shed light on clinical and basic research and provide the development of new clinical strategies for therapeutic intervention.