A typical behavior of microgel formation in emulsion polymerization, where a sufficient amount of crosslinker exists and no coagulation of particles occurs, is considered both theoretically and experimentally. It was found that the crosslinked polymer formation in emulsion polymerization is significantly different from that in homogeneous media. The important characteristics can be summarized as follows. (1) The crosslinking density level is fairly high even from very early stages of polymerization, (2) the weight-average molecular weight increases just linearly with monomer conversion, and (3) the formed molecular weight distribution (MWD) is rather narrow and the distribution shifts to larger molecular weights with preserving the narrow profile as polymerization proceeds. In a typical microgel formation in emulsion polymerization, each polymer particle essentially consists of a single crosslinked polymer molecule once stable polymer particles are formed.