Fields in the Language of String: Divergences and Renormalization

This paper describes my talk given to the 27th Johns Hopkins Workshop: Symmetries and Mysteries of M Theory, G\"oteborg, Sweden, 24-26 August, 2003. After a brief introduction to the lightcone worldsheet formalism for summing the planar diagrams of field theory, I explain how the {\it uv} divergences of quantum field theory translate to the new language of string. It is shown through one loop that, at least for scalar cubic vertices, the counter-terms necessary for Poincar\'e invariance in space-time dimensions $D\leq 6$ are indeed local on the worldsheet. The extension to cover the case of gauge field vertices will be more complicated due to the extra divergences at $p^+=0$ in lightcone gauge.