Liquid viscosity is a relevant parameter for acoustic cavitation and ultrasonically driven bubbles. However, its influence on bubble dynamics and bubble structure formation remains to a good part unexplored. As well, liquid viscosity effects on the bubble collapse hot spot, sonochemistry, and sonoluminescence are not fully understood yet. Here we report on results from a systematic project study that intends to fill some of these gaps. Focus is set on the peculiar individual and collective dynamics of bubbles in aqueous glycerine and ethylene glycol solutions under variation of viscosity, and further on sonoluminescence emissions of single bubbles and of multi-bubble fields.