In this talk I’ll give an introduction to intertwining operators for real reductive groups. After setting up principal series representations, I’ll construct the standard intertwining operator attached to the nontrivial Weyl element and explain its normalization and meromorphic properties. I’ll then describe how the finite R-group controls the commuting algebra and, in particular, determines the number of irreducible constituents at reducible parameters. The focus will be the concrete case of SL(2,R) where the formulas can be computed explicitly and the appearance of the R-group is especially transparent. Time permitting, I’ll indicate extensions to higher rank and briefly discuss how these operators inform the shape of local functional equations.