Group Theory Structures Underlying Integrable Systems

Different group structures which underline the integrable systems are considered. In some cases, the quantization of the integrable system can be provided with substituting groups by their quantum counterparts. However, some other group structures keep non-deformed in the course of quantizing the integrable system although their treatment is to be changed. Manifest examples of the KP/Toda hierarchy and the Liouville theory are considered.