This text presents, for the first time at an elementary level, current topics in applied mathematics such as singular perturbation, nonlinear wave propagation, bifurcation, similarity methods and the numerical solution of partial differential equations. It emphasizes the interdependency of mathematics and its application to physical phenomena, and is written in a style accessible to readers with a wide range of interests and backgrounds. There is also coverage of scaling and dimensional analysis, calculus of variations, Fourier and transform methods for partial differential equations and intergral equations.