Abstract: During the past decade it has been discovered that
techniques which were originally developed in the context of string theory
can be used for improving the efficiency of certain types of
computations in ordinary quantum field theory. I will discuss both the
original formalism of Bern and Kosower, based on the analysis of the
field theory limit of string theory amplitudes, and Strassler's more
elementary approach in terms of Feynman-Schwinger type worldline
path integrals. Some examples will be given demonstrating the
specific advantages of both formalisms, with an emphasis on
photon/gluon type amplitudes and effective actions in QED and QCD.