During the last several years remarkable progress has been made in understanding and solving a large class of two-dimensional nonlinear quantum field theories. First, there was the discovery and development of the inverse scattering method for solving partial differential equations [1,2], This powerful technique leads to complete integration [3] and explicit construction of soliton type solutions in many important nonlinear equations and has a wide range of applications in almost all areas of physics. Second, it has recently been shown that many examples of relativistic two-dimensional classical field equations can also be completely solved by this inverse scattering technique.