Line operators in supersymmetric gauge theories and the 2d-4d relation

This is the sixth article in the collection of reviews "Exact results on N=2 supersymmetric gauge theories", ed. J.Teschner. It is discussed how to use localisation techniques for the calculation of expectation values of Wilson and 't Hooft line operators. The results establish direct connections between supersymmetric line operators in gauge theories and the Verlinde line operators known from conformal field theory. Similar results can be used to strongly support connections to the quantum theories obtained from the quantisation of the Hitchin moduli spaces.