Technical Abstract: This chapter describes the neutron thermalization method for soil water content measurement, one of the most commonly used non-destructive methods. Principles, theory, major interferences, and statistics of neutron emission are discussed. Solutions to possible problems are given. Equipment and its use are described. A discussion of measurement volume and its effect on the evariance of water content values is included, along with comparisons to other non-destructive methods. Methods for field installations are described, with details of four separate methods useful in a variety of soils. A novel device ensuring accuracy of depth placement of the measurement probe is described. Both laboratory and field calibration methods are given, including a field calibration method for soils that vary greatly over a land surface. The field calibration method typically results in calibration root mean squared errors <0.01 m**3/m**3. Methods for checking calibrations, and methods for constructing calibration standards are described, as well as methods and equipment for transferring calibrations between meters. Use of the method in problem soils is discussed. Safety and environmental concerns are addressed; and the chapter ends with a discussion of advantages and limitations of the method. The chapter will be a useful reference for scientists, engineers and agricultural consultants needing to accurately measure water content in a variety of agricultural and non-agricultural situations, including dams, earthworks and mine spoils.