The ability to efficiently model coupled electron-photon transport is essential for determining the response of electronics components to nuclear radiation environments. Furthermore, to fully characterize the effect of many different radiation environments on a component, an adjoint transport capability is desirable. The theory of adjoint electron-photon transport is described with the CEPXSZONEDANT-LD discrete ordinates code package and the method is applied to a set of example problems representative of those encountered in radiation effects testing. Adjoint transport, in addition to efficiently modeling radiation source variations, can effectively model geometry variations for certain classes of problems. A new linear-discontinuous approximation of the continuous slowing down operator that introduces no upscatter is also developed.