  The object of this thesis is to study the spin-spin correlations for top
quark productions and their decay at polarized e^+e^- linear colliders. For the
analyses of the spin-spin correlations in top quark production, we introduce a
generic spin basis and show which spin basis is the most optimal. We discuss
the spin-angular correlations for the top quark decay, and demonstrate that the
directions of electro-weak decay products of polarized top quarks are strongly
correlated to the top quark spin. We also explain how to measure the top quark
spin using decay products. The spin correlations using the generic spin basis
are extensively studied at the next to leading order of QCD for top quark
productions at e^+e^- colliders. The radiative corrections induce an anomalous
\gamma/Z magnetic moment for the top quarks and allow for real gluon emissions.
Therefore they might change the leading order analyses. We show that higher
order effects on the top quark spin orientation are very small. The final
results are that the top (or anti-top) quarks are produced in an essentially
unique spin configuration for a particular spin basis even after including the
{\cal O}(\alpha_{s}) QCD corrections. Our results imply that measuring the spin
correlation for top quarks is very promising to reveal new aspects of the
Standard Model, as well as new physics beyond the Standard Model.
