So far there is no consensus on the fundamental mechanism of material removal in chemical-mechanical polishing (CMP). Some researchers model the CMP process based on the mechanism proposed by Kaufman et al. [1], who attribute the material removal from the wafer surface to chemistry-aided mechanical abrasions. Other researchers develop models for the CMP process based on a chemical tooth mechanism conjectured by Cook [2], who emphasizes the role of chemical reactions on the wafer surface. However, there is much evidence that both mechanisms are flawed. To clarify these issues, and reconcile the apparently contradictory conjectures [1,2], and provide a framework for further detailed modeling, a unified mechanism of material removal is proposed: the material at the wafer surface is removed by the strong shear stress from the non-Newtonian slurry flow in-between the wafer surface and the pad. Based on the proposed mechanism, a brief mathematical formulation is introduced to qualitatively describe the material removal rate. The proposed mechanism can be readily applied to explain the edge or the doming effect associated with non-uniform material removal for polishing blanket or patterned wafers.