  Running a future Linear Collider at the top pair threshold allows for precise
measurements of the mass, the widths and the couplings of the top quark. I give
a nontechnical review on recent theoretical developments and the theory status
in top threshold physics concerning QCD corrections and top quark finite
lifetime and electroweak effects. I also discuss threshold physics in the
context of measurements of the top Yukawa coupling from $e^+e^-\to t\bar t H$
and of squark pair production.
