One of the most useful ways that materials interact with light is Raman scattering, in which a photon creates or absorbs a lattice vibration. When the photon energy equals an electronic transition in the material (a “resonance”), the scattering can become much stronger. An outstanding mystery in 2D transition metal dichalcogenides has been the pronounced weakness of some excitonic resonances compared to others. The 2DCC-MIP team has developed an efficient first-principles way to calculate excitonic resonant Raman intensities, thereby explaining the puzzling near-absence of resonant Raman response around the A and B excitons (band-edge excitations with very strong optical absorption) and the pronounced strength of the resonant Raman response from the C exciton (which arises from parallel valence and conduction bands). These insights can now be carried to other semiconducting systems.