  The heavy quasiparticle bands in Kondo materials which originate in the
hybridization of f- and conduction electrons exhibit numerous, sometimes
coexisting, broken symmetry phases. Most notable are unconventional
superconductivity, itinerant small moment antiferromagnetism and hidden order
of higher order multipoles of f-electrons which all lead to a gapping of the
heavy bands. In rare cases the chemical potential lies within the hybridization
gap and the ground state is a Kondo semiconductor without ordering. The
dynamical magnetic response of such gapped f-electron systems has been
investigated with inelastic neutron scattering. It was found that collective
spin exciton modes which are due to residual quasiparticle interactions appear
below the threshold of superconducting or hidden order gap or directly the
hybridzation gap. The spin exciton resonance is commonly located around a zone
boundary vector $Q$ with nesting properties in the normal state. In the
superconducting case its appearance gives a strong criterion for the gap
symmetry requesting a sign change $\Delta_{{\bf k}+{\bf Q}}=-\Delta_{\bf k}$
due to the coherence factors. Therefore this many body effect with fundamental
importance may also be used as a tool to discriminate between proposed gap
models. While the spin resonance has been observed for many compounds we
restrict our discussion here exclusively to the small group of f-electron
superconductors CeCoIn5, CeCu2Si2 and UPd2Al3, hidden order Kondo compounds
CeB6 and URu2Si2 as well as the Kondo semiconductor YbB12 .
