Dispersive shock waves (DSWs) of the defocusing radial nonlinear Schrödinger (rNLS) equation in two spatial dimensions are studied. This equation arises naturally in Bose-Einstein condensates, water waves, and nonlinear optics. A unified nonlinear WKB approach, equally applicable to integrable or nonintegrable partial differential equations, is used to find the rNLS Whitham modulation equation system in both physical and hydrodynamic type variables. The description of DSWs obtained via Whitham theory is compared with direct rNLS numerics; the results demonstrate very good quantitative agreement. On the other hand, as expected, comparison with the corresponding DSW solutions of the one-dimensional NLS equation exhibits significant qualitative and quantitative differences. K E Y W O R D S nonlinear waves, nonlinear optics, water waves and fluid dynamics The applicability of the 2d NLS equation for Bose-Einstein condensate (BEC) wave functions in the appropriate geometries with the third coordinate axis being the axis of symmetry is well known and Stud Appl Math. 2019;142:269-313. wileyonlinelibrary.com/journal/sapm Company 269 270 ABLOWITZ ET AL. can be derived from many-body quantum dynamics, see, eg, Ref. 1. This equation can also describe deep water waves with sufficiently high surface tension. 2 A motivation to study the rNLS equation comes from the BEC experiments and the analysis in Ref. 3 where it was found numerically that the rNLS equation provides a good approximation to the dynamics.In the experiments of Ref. 3, an initial hump of the BEC density in the form of a ring was created by the laser beam effectively pushing the particles away from the center. Then, the BEC expanded radially. An additional radial parabolic potential that is absent in Equation 1 caused the BEC in experiments of Ref. 3 to move away from the center. Relative to this motion, however, the BEC expanded radially toward the inside that is what we consider analytically and numerically here.The dimensionless parameter characterizing dispersion (see Ref.3) was very small in these experiments, ≈ 0.012. With such a small value of Whitham theory, which is a nonlinear WKB-expansion in , is expected to be relevant. As pictures of the experiments show, in the expansion, large oscillations of the BEC density were created, which implies a dispersive shock wave (DSW) started from the initial density jump. The oscillations formed a number of concentric rings, ie, the DSW propagation was indeed radial with high degree of accuracy. Similar concentric rings forming a radial DSW were observed in nonlinear optics experiments. 4 However, in Ref.3, only the one-dimensional NLS equation was treated analytically. Whitham modulation theory for the (1 + 1)-dimensional NLS (1d NLS) equation (see Refs. 5 and 6) was applied to this problem. While qualitative agreement with experiments and direct simulations was found, and the solution/experiments exhibit character of a DSW, the analytical results did not always correspond closely (see, eg, figure 24 of Ref. 3). N...