What do mesons have to do with nuclear structure?

The theory of nuclear structure (binding, low energy spectra, transitions, etc.) depends on nucleon-nucleon (NN) interactions. The meson theory of NN interactions has predictive power for NN scattering, and partial success when applied to the theory of nuclear structure. Is it possible to test this theoretical picture -- by direct experimental interaction with mesons in nuclei? Some experimental searches for the `pion excess' in nuclei have ambiguous results. How sensitive are such experiments to the mesonic aspects of nuclear structure? These questions are addressed in this talk. More details and references are given in Reference [1].