Theoretical aspects of W-pair production in e+e- collisions
  The most interesting theoretical features of W-pair production in e+e- collisions are reviewed. Based on an analysis of on-shell W-pairs, it is shown that the mere inclusion of leading $O(\alpha)$ corrections--such as initial-state radiation, effects from the universal quantities $\Delta\alpha$ and $\Delta r$, and the Coulomb singularity--cannot be expected to approximate the $O(\alpha)$-corrected cross-section of $e^+e^-\to W^+W^-\to 4f$ to better than 1-2% for LEP2 energies. The importance of the gauge-invariance problem, arising from the introduction of finite decay widths, is discussed. The simplest consistent method to include $O(\alpha)$ corrections at least to the doubly resonant contributions, viz. a pole expansion around the double resonance, is also briefly described. 
Stefan Dittmaier