2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/40406In this talk I briefly summarize different models for $σ^{tot}_{2 γ}$ ($e^+e^- \to γγ\to$ hadrons) and contrast model predictions with the data. I will then discuss the capability of the future $e^+e^-$ and $γγ$ colliders to distinguish between various models and end with an outlook for future work.10 pages, 3 figures, LaTeX, uses aipproc.cls and aipproc.sty. Talk to appear in the proceedings of International Linear Collider Workshop (LCWS) 2000, October 26-30, 2000, FermilabHigh Energy Physics - Phenomenologytext