A simple and general method for evaluating the condition of gelation for three dimensional polycondensation and copolycondensation reactions is presented. By reasonable development of Flory's method

the author suggested a new concept for the critical condition of gelation

namely

that the probability for a central branch point to be connected to themselves attains unity. According to this concept without referring to the molecular size distribution function

equations for the gel point for various generalized reaction types were obtained

which include almost all types of reactions encountered in practce. The results previously obtained by other authors appear as special cases of this paper.