Phase-field modeling, which introduces the regularized representation of sharp crack topologies, provides a convenient strategy for tackling 3D fracture problems. In this work, an adaptive isogeometric-meshfree approach is developed for the phase-field modeling of brittle fracture in a 3D polycrystalline material. The isogeometric-meshfree approach uses moving least-squares approximations to construct the equivalence between isogeometric basis functions and meshfree shape functions, thus inheriting the flexible local mesh refinement scheme from a meshfree method. This refinement scheme is improved by introducing an error estimator that includes both the phase field and its gradient. With the present approach, numerical implementations of the adaptive phase-field modeling that introduces the anisotropy of fracture resistance in polycrystals are proposed. In this way, propagating cracks can be dynamically tracked, and the mesh near cracks is refined in a meshfree manner without requiring a priori knowledge of crack paths. Furthermore, the intergranular and transgranular crack propagation patterns in polycrystalline materials can be simulated by the present approach. A series of numerical examples that deal with the isotropic and anisotropic fracture are investigated to demonstrate the robustness and effectiveness of the proposed approach. K E Y W O R D S adaptivity, anisotropy, isogeometric-meshfree approach, phase-field modeling, polycrystalline material 1 INTRODUCTION Fracture behaviors of engineering materials and structures, such as crack initiation, propagation, coalescence, and branching, have been extensively investigated by two types of numerical models: the discrete and diffusive models. The discrete model treats cracks as moving boundaries by constructing discontinuous displacement fields. Within the framework of a discrete model, a variety of methods have been developed, such as the extended finite element method (XFEM), 1 cohesive zone method, 2,3 extended isogeometric analysis (XIGA), 4 and extended meshfree method. 5 As a discrete model requires descriptions of crack surfaces, it suffers from low computational efficiencies induced by the tracking of complex 5042