There has been recent increasing interest in the acoustic properties of suspensions for applications such as ultrasonic particle size and concentration instrumentation. This paper aims to summarize what is known about the acoustic properties of suspensions of solids in a liquid and aims to identify the methods that enable useful information to be extracted from sound speed and attenuation information such as particle size, concentration, and the mechanical properties of the constituents. The paper identifies regimes of sound propagation and present models for these that can be used for size characterization of slurries.