The human face is the oldest and most universal emotion communication system, argues Prof. Freitas-Magalhães, the world's leading expert for Neuroscience and Biobehavioral Psychology and the Encyclopedia of Human Behavior, by Elsevier, Oxford, in his pioneering and extraordinary book on facial expression of emotion. In this book, the author leads the reader on a rigorous and fascinating journey from Charles Darwin's first intuitions to the latest advances in contemporary neuroscience, revealing how the face asserts itself as a direct mirror of the emotional brain. Based on decades of scientific research, the biological, psychological and cultural foundations of facial expression are explored, as well as the automatic mechanisms that give rise to visible emotions. Integrating pioneering theories such as Facial Brain Theory and using the advanced F-M FACS 5.0 system and its evolution to F-M FACS 6.0, the book proposes a new reading of human emotion: measurable, codificable and scientifically validated. Throughout the pages, the role of neuromicroexpressions as biomarkers of neural activity is evidenced, opening new perspectives for research, clinical practice and emotional artificial intelligence. More than an academic contribution, this book asserts itself as a milestone in the history of the science of emotion, redefining the way we understand the relationship between the brain, the face and human behavior.