The Singular Behaviour of QCD Amplitudes at Two-loop Order

We discuss the structure of infrared singularities in on-shell QCD amplitudes at two-loop order. We present a general factorization formula that controls all the $\text{ep}$-poles of the dimensionally regularized amplitudes. The dependence on the regularization scheme is considered and the coefficients of the $1/\ep^4, 1/\ep^3$and$1/\ep^2$ poles are explicitly given in the most general case. The remaining single-pole contributions are also explicitly evaluated in the case of amplitudes with a $q\bar{q}$ pair.