The sales figures for smartphones continue to rise exponentially. Tablet computers are showing a similarly phenomenal adoption rate and are replacing laptop computers in many areas of life. We can imagine a time when nearly everyone is carrying around a powerful computer in the form of a smartphone or a tablet. The term mobile device is used to cover such devices. Typically, an app (an application program) for a smartphone or tablet has to be developed in a PC and transferred to the mobile device later. But does it have to be that way? The TouchDevelop project at Microsoft Research has proved that the answer is No. TouchDevelop is a programming environment that runs on all mobile devices. It allows a script to be developed on a mobile device, or on a PC, and to be run on any mobile device or a PC. After releasing the app in 2011 when it was available only for the Windows Phone, the overwhelming response was a big surprised us: more than 200,000 users downloaded the app and they published more than 10,000 scripts written entirely on phones. Since then, TouchDevelop has been made available in a form that runs on PC, Mac and Linux platforms, and on iPad, iPhone, iPod Touch and Android devices. TouchDevelop is truly a portable development environment for creating portable apps.

Mobile devices represent the latest in technology. Furthermore, many students actually own their own smartphone. High school teachers and college or university instructors love the idea of using the latest technology to engage their students. While they may be experts in the field of teaching programming, many teachers appreciate guidance on how to navigate a complex app like TouchDevelop: its visual program editor is designed for touchscreens and uses different editing paradigms from a traditional keyboard-based text processor. Another opportunity and challenge is how to make use of some of the sensors that a modern mobile device has to offer.