We show with several examples that renormalization group (RG) theory c
an be used to understand singular and reductive perturbation methods i
n a unified fashion. Amplitude equations describing slow motion dynami
cs in nonequilibrium phenomena are RG equations. The renormalized pert
urbation approach may be simpler to use than other approaches, because
it does not require the use of asymptotic matching and yields practic
ally superior approximations.