Book excerpt: This book presents the state of the art, principles and ideas of Electrophotonic analysis based on Gas Discharge Visualisation (GDV) technique, known as well as Electrophotonic Imaging (EPI). This approach, celebrating now 15 years after developing the first GDV instrument, has a strong scientific foundation with thousands of researchers, doctors and practitioners using it in the world. Electrophotonic methods allow to study Energy Fields of humans, water, materials and environment. Conceptual background and practical approaches are presented in this book.