<p>The state of water and its transformation exert strong controls on the properties of soils, which has long been concerned in soil science and engineering practice. Under various environmental conditions, the water in soils may undergo dynamic migration and phase changes, for which conventional methods usually lack sufficient resolution or provide inaccurate results. To resolve these issues, the low-field nuclear magnetic resonance (NMR) technology capable of directly detecting hydrogen nuclei in water, has been introduced in the field of petroleum and geotechnical engineering with successes. Even though low-field NMR has shown its great potentials in identifying and quantifying fluids of different constituents in geotechnical porous media, this technique has not been fully explored in investigating the state of water in clayey soils, and very limited works have been made to summarize the existing progresses. In this work, we conduct a systematical review on the application of low-field NMR in investigating the state of water in clayey soils. We first summarize practical strategies for optimizing acquisition parameters and measurement sequences. Next, we review the application of low-field NMR techniques in quantifying the content, detecting the migration, and tracking phase transition processes of water in clayey soils, with particular emphasis on how <i>T</i>₁ and <i>T</i>₂ relaxation times enable differentiation of adsorbed, capillary, and bulk water. We then discuss the advantages and limitations of current experimental methods. This paper finally provides recommendations for advancing the use of low-field NMR technology in clayey soils.</p>