This chapter presents the foundational principles of computational fluid dynamics for modeling particle–fluid systems. It introduces the governing equationsGoverning equations of fluid flow including the continuity and momentum equations and details the critical particle–fluid interaction forcesParticle-fluid interaction forces, with a focus on drag, lift and other relevant forces. The turbulence modeling, covering the Reynolds-Averaged Navier–Stokes approach, large eddy simulation, and direct numerical simulation, alongside guidelines for model selection are also introduced. Furthermore, the chapter explains essential numerical techniques, including spatial and temporal discretization methods. The complete computational fluid dynamics workflow is described, encompassing geometry modelingGeometry modeling, mesh generationMesh generation, the implementation of boundary conditionsBoundary conditions and specific near-wall treatment strategies required for accurate simulations.