Derivation of the Lamb shift using an effective field theory

We rederive the O(alpha(5)) shift of the hydrogen levels in the nonrecoil l imit (m(e)/m(P) --> 0) using an extension of nonrelativistic QED (NRQED), a n effective field theory developed by Caswell and Lepage. Our result contai ns the Lamb shift as a special case. Although this calculation is not new, it is presented here for the first time using the modern language of effect ive field theories. It clearly illustrates the usefulness of applying a mul tipole expansion to the NRQED vertices.