Review on Physics of $e^+e^- \to t\bar{t}$ Near Threshold$^*$
  We review the recent developments of studies on $e^+ e^- \to t\bar{t}$ in the threshold region. It has been shown that the top threshold cross sections will be able to provide many important and interesting physics. Due to the large mass and the large decay width of top quark, there will appear a number of unique features at top threshold. First, theoretical background is summarized. Then we present observables that are typical to the top threshold region, and discuss the physics that can be extracted. Also, we list the results of the recent parameter determination study taking a sample case of $m_t = 170$~GeV. 
Y. Sumino