Two-Dimensional Integrable Systems and Self-Dual Yang-Mills Equations

The relation between two--dimensional integrable systems and four--dimen\-sional self--dual Yang--Mills equations is considered. Within the twistor description and the zero--curvature representation a method is given to associate self--dual Yang-Mills connections with integrable systems of the Korteweg--de Vries and non--linear Schr\"odinger type or principal chiral models. Examples of self--dual connections are constructed that as points in the moduli do not have two independent conformal symmetries.