Recent progress in theoretical calculations of two-photon exchange in electron-proton scattering

Two-photon exchange (TPE) effects are relevant for extractions of proton form factors at moderate to high $Q^2$, and of the proton radius at very low $Q^2$. Recent experiments to directly measure hard TPE effects by comparing elastic $e^+-p$ to $e^--p$ scattering have motivated further theoretical work in this area. In this contribution I give an overview of recent progress in theoretical calculations of TPE effects, focussing on the contributions of intermediate states in the resonance region $W\le 2$~GeV$^2$ using the CLAS parameterization.