The mathematical background to the topic of asymptotic approximation methods for the solution of ordinary and partial differential equations is given first. These methods are then applied to several examples of problems from astrophysical fluid (and magneto-fluid) dynamics. An entire chapter is devoted to each topic and among them are - accretion disk boundary layers, fronts in thermally bistable interstellar medium; ideas from geophysics (shallow water theory) applied to modeling accretion disks; the discovery of transient perturbation growth in accretion disks, a growth than...