The universe is the most wonderful hydrodynamics laboratory imaginable. Every kind of flow we observe in terrestrial environments occurs in the cosmos an a truly grand scale. Supersonic motion, magnetohydrodynamic flows, turbulence of every variety, and instabilities of perplexing richness all present themselves to the alert eye. It is the purpose of this book to introduce these processes to astronomers in the hope that they will find the tools necessary for understanding both their observations and the related theoretical literature. Since the first edition of the book, the expansion in instrumentation – wavelength coverage, spatial resolution, and sensitivity – has been astounding. Interferometric optical spectropolarimetry is now possible, virtually the entire electromagnetic spectrum is avaialble. Not only can we determine velocities and observe structure, we can also get true flux measurements for objects fainter than ever before accessible.