The general topic is the generation of sound by, and the propagation of sound in fluid flows. These include flows around machinery, airfoils, and other man-made objects, as well as the flow of wind around obstacles. The chapters in this volume represent the results of a workshop discussing mathematical and computational aspects of the interaction of sound with air at the Institute for Computer Applications in Science and Engineering, at the NASA Langley Research Center. Topics covered include: classical theoretical approaches (which can serve to supply both efficient formulations for computational implementation and the boundary conditions that are essential for accurate simulations); mathematical aspects of acoustics; validation methods (including stability considerations, gridding, and back-reactions); direct simulation (the use of computational fluid dynamics to describe the generation, transmission, and radiation of sound in fluid flows); and computational methods for unsteady compressional flows. The topics covered in this book will be of interest to aerospace and other mechanical engineers interested in modeling and reducing noise generated by fluid flows such as propeller noise from windmills, sonic booms due to aircraft, or buildings that sing in the wind.