  We discuss different formulations and approaches to string theory and $ 2d$
quantum gravity. The generic idea to get a unique description of {\it many}
different string vacua altogether is demonstrated on the examples in $ 2d$
conformal, topological and matrix formulations. The last one naturally brings
us to the appearance of classical integrable systems in string theory. Physical
meaning of the appearing structures is discussed and some attempts to find
directions of possible generalizations to ``higher-dimensional" models are
made. We also speculate on the possible appearence of quantum integrable
structures in string theory.
