The Dynamics of Quantum Fluids

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.