Abstract Dielectric anisotropy in ice alters the propagation of polarized radio waves, so polarimetric radar sounding can be used to survey anisotropic properties of ice masses. Ice anisotropy is either intrinsic, associated with ice‐crystal orientation fabric (COF), or extrinsic, associated with material heterogeneity, such as bubbles, fractures, and directional roughness at the glacier bed. Anisotropy develops through a history of snow deposition and ice flow, and the consequent mechanical properties of anisotropy then feed back to influence ice flow. Constraints on anisotropy are therefore important for understanding ice dynamics, ice‐sheet history, and future projections of ice flow and associated sea‐level change. Radar techniques, applied using ground‐based, airborne, or spaceborne instruments, can be deployed more quickly and over a larger area than either direct sampling, via ice‐core drilling, or analogous seismic techniques. Here, we review the physical nature of dielectric anisotropy in glacier ice, the general theory for radio‐wave propagation through anisotropic media, polarimetric radar instruments and survey strategies, and the extent of applications in glacier settings. We close by discussing future directions, such as polarimetric interpretations outside COF, planetary and astrophysical applications, innovative survey geometries, and polarimetric profiling. We argue that the recent proliferation in polarimetric subsurface sounding radar marks a critical inflection, since there are now several approaches for data collection and processing. This review aims to guide the expanding polarimetric user base to appropriate techniques so they can address new and existing challenges in glaciology, such as constraining ice viscosity, a critical control on ice flow and future sea‐level change. Plain Language Summary Radar is commonly used to examine into and beneath glaciers and ice sheets where direct observations are difficult to obtain. In this review, we focus on one specific radar application, polarimetry, which analyzes the differences between radar measurements with different antenna orientations. Radar polarimetry is primarily used to measure the orientation of ice crystals, the pattern of which can: (a) influence the flow of an ice mass, an important factor controlling future global sea levels; and (b) record past ice flow, providing insights into past climate on geologic timescales, up to tens of thousands of years. Recent innovations in radar tools have led to accelerated application of polarimetry in glaciological research, and future innovation will only expand the use case further. This review aims to act as an introduction to those unfamiliar with radar polarimetry, as a call to expand this small scientific community within glaciology and extend the relevant scientific applications, and as a guide to users of these techniques, not only in how they have been used historically, but also in the physical context for how best to interpret the polarimetric radar signature. Key Points Individual ice crystals are dielectrically anisotropic, so polarimetric radar can be used to assess patterns in the bulk crystal orientation Crystal orientation depends on past deformation and affects viscosity, so polarimetric radar can constrain ice motion in the past and future Anisotropy in dynamic parts of Earth's ice sheets and within planetary ices are knowledge gaps and therefore are new research foci