An approximate method especially suited to near‐continuum flows is developed. The method is applied to the case of Couette flow with arbitrary specular and diffuse reflection. The result is in very close agreement with all known limits. In the case of purely diffuse reflection the approximate theory leads to a slip coefficient which is within112%of the exact value. The analytical behavior in the neighborhood of the walls is exactly described. The limit of purely specular reflection is exactly described by the approximation method. The method only involves elementary calculations.