The purpose of this paper is to explore the dynamic feedback stabilization problem for general nonlinear systems extending previous works of Artstein, Sontag, and the author. First, sufficient conditions for global stabilization by smooth dynamic feedback are provided concerning a wide class of triangular systems, where the linearization at the equilibrium is controllable. For the general nonlinear case, we derive a necessary and sufficient condition for global stabilization by means of an almost smooth dynamic feedback.