This book provides a detailed review of the modern theories dealing with the structure and properties of water. It also presents an analysis of the research on the effect of activated water on biological systems such as animals, microorganisms, and plants. The results of experiments on the influence of activated water on pure microbiological cultures and their natural associations are described, the studies being carried out under both aerobic and anaerobic conditions. The results demonstrate a significant influence of activated water on higher plants (vegetable crops), sterile plants, and callus tissues. It is shown that the activation of water under definite conditions gives rise to the appearance of very strong bactericidal properties: activated water inhibits the development of pathogenic microbiological cultures by tens and hundreds of times more strongly, and can be used for sterilization. In addition, a potent positive effect of activated water on the prevention and treatment of cancer in mice has been observed, and its efficacy compared to that of chemotherapy is discussed in the book. The information provided in this book is supported by intensive experimental data and developed theories. The research programs were conducted at the authors' laboratories in Ukraine and Russia as well as at research facilities located in the USA. Introduction to the Theory of Water Memory and General Principles of Water Activation Molecular Resonance Effect Technology as the Basic Method for Activation of Liquid Substances Study of the Physical Properties of MRET Activated Water Influence of MRET Activated Water on the Growth of Higher Plants Effects of MRET Activated Water on Microbial Culture and Natural Microbial Associations Examination of the Influence of MRET Activated Water on Prophylaxis and Treatment of Oncology Effect of MRET Activated Water on Staphylococcal Infection in vivo in Animal Model (on the Cells of Immune System) and in vitro on the Culture of Staphylococcus aureus Wood-46 The Possible Mechanisms of Effects of Activated Water on Biological Systems Conclusions and Recommendations