The paper examines the history of the development of studies of the state of water in plants, outlines the modern (as of 1974) data necessary for plant physiologists on the state (physical properties and structure) of pure water, water in electrolyte and non-electrolyte solutions, as well as current hypotheses about the state of water in biological objects. The results of studies of the state of water in plants at the molecular level using methods of dielectric and infrared spectroscopy (DS and ICS) and nuclear magnetic resonance (NMR, spin echo) are given. The possibility of studying the state of water in parts of a plant cell is shown and data on the state of water in chloroplasts are given. The relationship of the molecular dynamics of water with the physiological processes of plants (enzyme activity, respiration, photosynthesis, resistance to drought and frost) is considered.