It has recently been shown that the identification of a linear time-invariant plant using closed-loop measurements with a known linear controller can be effectively tackled by regarding the unknown plant as a member of the set of all plants stabilized by the known linear controller. This set is parametrized by a Youla-Kucera parameter, itself a stable transfer function which, it turns out, can be identified using open-loop techniques. This paper generalizes the parametrization idea to nonlinear plants, and treats identification of nonlinear plants.