Review of new physics effects in t(t)over-bar production

Both CDF and Dempty set report a forward-backward asymmetry in t (t) over bar production that is above the standard model prediction. We review new physics models that can give a large forward backward asymmetry in t (t) over bar production at the Tevatron and the constraints these models face from searches for dijet resonances and contact interactions, from flavor physics and the t (t) over bar cross section. Expected signals at the LHC are also reviewed.