A variety of experiments that have been undertaken to investigate the acoustic characteristics of bubble clouds will be described. These experiments have involved both passive acoustic emission, in which the radiated noise is measured from a bubble cloud that is being produced, and active acoustic scattering, in which sound waves are scattered from a similarly produced bubble cloud after it has ceased to radiate emissions. It appears that the dominant acoustic characteristic of these clouds is that they readily emit, and can easily be stimulated into emitting, low-frequency sound by the collective oscillations of the bubbles within the cloud. This mode of oscillation [see papers by Prosperetti and by Carey and Browning in SeaSurfaceSound, edited by B. R. Kerman (Kluwer Academic, Dordrecht, 1988)] appears to provide a physical mechanism for a broad range of ambient noise emissions in the ocean and may play an important role in low-frequency active scattering from the ocean surface. [Work supported by ONR and ONT.]