Book excerpt: This book is about the theory of Hot and Cold, a mutual fundamental base of traditional medicines all around the world. The theory describes the dynamic balance state of the body on the axis of hot and cold for each individual and proposes the fact that deviation from this equilibrium is a predisposing factor for diseases. Such an approach helps practitioners to provide treatments tailored to the patient’s condition, not the disease. This book, for the first time, has gathered native descriptions of Hot and Cold theory in different traditional medicines, including traditional Chinese medicine, Persian (Humoral, Unani) medicine, Ayurvedic medicine and Latin American and Caribbean medicines. After defining the common ground, contemporary research - in nutrition, pharmacology, physiology and systems biology - has been explored using scientific methodology. This work is the result of an international collaboration of more than 30 scientists and scholars with high reputations in their fields. Hot and Cold theory, as a holistic individualized approach in prevention, diagnosis and treatment, can be merged into the novel fast-paced concepts in systems biology and precision medicine. Through this bridge, the authors propose that the Hot and Cold theory should be revisited more deeply by medical scientists, who are the main audience of this book, to pave the way towards integrated holistic personalized medicine.