In this paper right coprime factorization results are derived for i. general class of nonlinear plants and stabilizing feedback controllers Both input-output descriptions and state space realizations of th(plant and controller are used. It is first shown that if there exist stable right coprime factorizt ions for the plant and controller, and if a certain matrix of nonlinear operators has a stable inverse then the feedback system is well-posed and internally stable. The links between the right and left coprime factorization for a stable plant controller pair will be explored for this purpose. A generalization of the notion of linear fractional maps is explored as a means of characterizing the class of plants stabilized by this controller, and dually classes of controllers which stabilize the plant. It is then shown how to apply this theory to nonlinear plants which have a state space realization of a given form. It is also shown that if there exists a stabilizing state feedback for a plant in the class of int crest, then there exists a right cop rime factorization for the plant. Additionidly if there exists a stabilizing output injection, then there will exist a stabilizing controller with a right coprime factorization. An important sasumption in this work is to assume that the plant and controller have the same initial conditions, an approach is developed to allow for the stabfization of the plant by a controller with a different initial condition. A similar approach may also be used to stabilize a plant which has unmodeled dynamics. These results, of course, specialize to familiar linear system ones, and just as such linear systems results have had a wide application in robust and adaptive control system design, it is believed that the results developed here will facilitate the development of corresponding nonlinear robust and adaptive control system design.