This paper by A. Cemal Eringen introduces the theory of micropolar fluids, which are fluids that respond to micro-rotational motions and spin inertia, allowing them to support couple stress and distributed body couples. The author derives the equations of motion, constitutive equations, and boundary conditions for these fluids. The thermodynamic restrictions on the viscosity coefficients are studied in detail, and the field equations for density, velocity vector, and micro-rotation vector are obtained. The paper also presents the solution for channel flow, which exhibits interesting phenomena such as reduced skin friction and the presence of distributed couples. The theory is applicable to fluids like liquid crystals and certain polymeric fluids, and it provides a new framework for understanding and predicting the behavior of these fluids. The paper concludes with a discussion on the potential applications of micropolar fluid theory in fluid mechanics and turbulence theory.This paper by A. Cemal Eringen introduces the theory of micropolar fluids, which are fluids that respond to micro-rotational motions and spin inertia, allowing them to support couple stress and distributed body couples. The author derives the equations of motion, constitutive equations, and boundary conditions for these fluids. The thermodynamic restrictions on the viscosity coefficients are studied in detail, and the field equations for density, velocity vector, and micro-rotation vector are obtained. The paper also presents the solution for channel flow, which exhibits interesting phenomena such as reduced skin friction and the presence of distributed couples. The theory is applicable to fluids like liquid crystals and certain polymeric fluids, and it provides a new framework for understanding and predicting the behavior of these fluids. The paper concludes with a discussion on the potential applications of micropolar fluid theory in fluid mechanics and turbulence theory.