  These lecture notes provide an introduction to non-equilibrium superfluid
3He, with applications to high-frequency excitations, including aspects of
symmetry breaking in 3He and its effects on collective mode dynamics. In 1957
Landau predicted that liquid 3He would support propagating shear waves at low
temperatures, i.e. a transverse sound mode. Such waves have recently been
observed at low temperatures in the superfluid B-phase of liquid 3He. These
observations provide a beautiful example of the effect of spontaneous symmetry
breaking in condensed matter. I discuss the theory of transverse wave
propagation in 3He and the recent detection of these waves by magneto-acoustic
rotation of the 3He polarization in a magnetic field.
