A review of the hydrodynamic interpretation of the various sound or collective modes which propagate in superfluid helium will be presented. These will be separated into two categories: (a) bulk geometries, (b) helium confined between walls as narrow as 10 Å. As regards the bulk, the thermal propagating waves (second sound) as well as ordinary density waves will be discussed. For the confined geometries third sound (analogous to long gravity waves with the restoring force replaced by the van der Waals attraction to the substrate) and fourth sound (another pressure wave propagated through a modified compressibility) will be discussed. Use of the propagation and attenuation of sound to measure various thermodynamic properties will be explored.