Abstract: Soil moisture is a key parameter influencing hydrological processes, agricultural production, ecological stability, and engineering safety. Its accurate measurement and dynamic monitoring have long been central topics in earth and environmental sciences. This review outlines the development of soil moisture monitoring technologies and proposes a classification framework based on measurement principles and application contexts, including laboratory benchmark methods, in situ sensing technologies, and remote-sensing retrieval techniques. The effects of soil physicochemical properties, environmental conditions, and methodological limitations on measurement accuracy are examined. Special attention is given to the mechanisms governing the separation of unfrozen water and ice content in frozen soils and the associated quantitative models. By comparing laboratory and in situ approaches and discussing multi-method integration in typical scenarios, the review clarifies the complementarity and applicability boundaries of different techniques. Future perspectives are highlighted, including multi-sensor fusion and air–space–ground data assimilation, AI-assisted calibration and interpretation, and cross-scale monitoring and simulation for complex environments. These insights support a deeper understanding of soil moisture processes and provide technical references for engineering, agriculture, and ecological management.