This document discusses methods for estimating soil moisture content. It defines soil moisture as the water held in the spaces between soil particles, particularly in the top 200 cm that is available to plants. There are direct methods that measure the moisture content through gravimetric techniques like oven drying samples, and volumetric methods using bulk density. Indirect methods measure water potential or tension, including tensiometers, gypsum blocks, and neutron probes. Remote sensing techniques estimate soil moisture from visible/infrared reflectance, thermal infrared surface temperature, and passive/active microwave emissions and backscattering related to dielectric properties.