Waterjet technology involves complex flow phenomena, which include supersonic, turbulent, compressible, and three-phase interactions. This book, by the editor and colleagues, distills three decades of R&D expertise from Flow Industries, Inc. and OMAX Corp., based in Kent, Washington, USA. Organized into 10 sections and 32 chapters, it blends physical experiments and limited computational fluid dynamics analyses as R&D methodologies. Through flow visualization and probe measurement, the book characterizes waterjet geometry, water-droplet and abrasive speeds, surface roughness and edge qualities of machined parts, and more. It showcases advancements in micro abrasive-waterjet technology, recognized as a 2016 R&D 100 Awards finalist and honored with the 2016 Tibbitts Award from the U.S. Small Business Administration.