Theoretical studies on the motion of the red blood cell in the blood flow are surveyed, in relation to the recent advance in experiments. One of the most realistic models for the red blood cell, which contains a viscous fluid interior enclosed by a flexible membrane, has enabled detailed description for the peculiar behavior of the red blood cell in microvessels and in shear flow. For quantitative comparison between theory and experiment, there is a need for the development of theoretical analyses including asymmetric flow in microvessels and cell motion under cell-cell interactions.