Summary of Working Group 1: Theory Part

I will summarize theoretical issues in Working Group 1 at Nufact'01. Although there may not be complete agreement yet on the exact optimum baseline $L$ and the muon energy $E_\mu$ for measurements of the CP phase at a neutrino factory, all the works done so far indicate that the optimum set ($L$, $E_\mu$) tends to be smaller than (3000km, 50GeV) if the uncertainty of the matter effect is assumed to be larger than $\pm$5% or the background fraction is much larger than $10^{-5}$.