Pure Data (Pd) is a graphical programming environment for audio and more; libpd is a wrapper that turns Pd into a portable, embeddable audio library. Brian Eno’s soundtrack of the game Spore is generated by Pure Data. Inception The App is based on libpd and has been downloaded more than three million times. The popular RJDJ also uses the technology. The purpose of this book is to present tools and techniques for using Pure Data and libpd as an audio engine in mobile apps (for Android and iOS). The tools described are perfect for the sound engine for a game or for transforming a phone or tablet into an experimental instrument. After reading the book, audio developers will know how to prepare Pd patches for use with libpd, and app developers will know how to use all features of the libpd API. Readers with some experience in both computer music and mobile development will be able to create complete musical apps. The book includes a crash course in Pd, just enough to allow readers to make sounds and control them, as well as a discussion of existing solutions for rapidly deploying Pd patches to mobile devices. An introduction to Android or iOS development is beyond the scope of this book; readers will be expected to have a basic grasp of their platform of choice, including a working development setup. The book will, however, explain how to integrate libpd into an existing setup. A number of sample apps, ranging from minimal to full featured, for both Android and iOS, will illustrate all major points.