The string equation and solitons

We present a brief survey of the results of the Theory of Solitons from the viewpoint of the periodic theory including some new results in the theory of 2-dimensional periodic Schrodinger Operators. The main subjects are: Periodic Solitons and Algebraic Geometry, The Theory of Solitons and the String equation, Topologically trivial and nontrivial periodic two-dimensional Schrodinger operators and Riemann surfaces and Cyclic and semicyclic chains of Laplace transformations (new results of the present author and A.Veselov)