This paper reviews the recent progress of experimental and theoretical works on the understanding of the pattern selection in dendritic crystal growth. The dendritic tip is usually an paraboloidal revolution, whose radius of curvature and the growth speed are experimentally determined by the undercooling or the supersaturation. An intuitive argument is presented that geometric mean of macroscopic diffusion length and microscopic capillary length is the length scale of this physical system. Also the mechanism and the nature of sidebranching instability are discussed.