Results of theoretical and experimental studies of the thermal self-action
of powerful acoustic beams in high-viscosity liquids are discussed. A theor
y of acoustic self-focusing and serf-induced transparency that occur in liq
uid as a result of the thermal nonlinearity is presented. The conditions fo
r the observation of these effects are determined. The basic experiments on
the thermal self-action of sound are described. The most promising applica
tions of the aforementioned nonlinear acoustic effects are analyzed.