Sonication (or ultrasound irradiation) has emerged as a potential technique for the intensification of diverse physical/chemical/biological processes. In recent years, sonication has been applied in the synthesis of liquid biofuels, such as biodiesel, and bioalcohols, such as ethanol. The process of bioalcohol synthesis comprises four steps, viz. acid pretreatment, alkaline delignification, enzymatic hydrolysis and fermentation. Significant literature has been published in the last decade on the application of ultrasound for the intensification of all the steps of bioalcohol synthesis. In this paper, a critical review and analysis of the literature on ultrasound-assisted bioalcohol synthesis has been presented. This review has addressed all four steps of bioalcohol synthesis. Essentially, the literature in the areas of ultrasound-assisted biomass pretreatment, delignification and hydrolysis has been reviewed, followed by an analysis of the literature on ultrasound-assisted fermentation. Finally, the mechanistic investigations of the various steps of bioalcohol synthesis have been reviewed, highlighting the synergistic links between the physical/chemical effects of ultrasound and cavitation and the basic physical/chemical mechanisms of the steps of bioalcohol synthesis. The critical analysis of the literature in this review has not only demonstrated the efficacy of ultrasound in the intensification of all the steps of bioalcohol synthesis, but has also brought to light the underlying mechanistic issues; this could provide guidelines for the design and optimization of commercial scale bioalcohol processes.