  We review experimental and theoretical progress in the physical description
of the dynamics of the quantum fluids \he4 and \he3. Historically, the
elementary excitations in these systems have been identified as phonons and
rotons and, in \he3, collective zero sound and spin-fluctuations. Both recent
high-precision measurements and theoretical methods have shown that the
dynamics of these systems is actually very rich as will be discussed in detail
in the body of this contribution.
