Abstract: In this paper, first we briefly survey the evolution of the theory of Backlund transformation, then a new method for seeking Backlund transformations for differential equations, the Wahlquist-Estabrook procedure, is outlined. This method is the most effective approach to date for treating Backlund problem of differential equations. Although it is theoretically applicable to systems of partial differential equations with any dimensions, this method is actually limited for problems which are mainly two-dimens...