In the developing area of nonlinear mathematics, there are a large number of classes of nonlinear equations which have received attention. This collection of 11 articles addresses a number of physically motivated systems for which considerable theory is available, such as reaction-diffusion systems and elasticity. Theories that are available for wider classes of equations include discussions of Lie symmetries, improperly posed problems and integrable nonlinear equations. The main purpose of the book, however, is to address real situations. The range of applications presented to the reader is intended to help to make the developing studies of nonlinear mathematics more understandable.