Have you ever wanted to build your own mobile apps? App Inventor, a free and revolutionary online program from MIT, lets you do just that. With the help of this companion guide chock-full of colorful graphics and easy-to-follow instructions, readers can learn how to create six different apps, including a working piano, a maze game, and even their own chat app to communicate with friends—then use what they’ve learned to build apps of their own imagination. User-friendly code blocks that snap together allow even beginners to quickly create working apps. Readers will also learn about young inventors already using their own apps to make a difference in their communities, such as the girls from Moldova whose app helps alert residents when local well water is contaminated. Or the boys from Malden, Massachusetts, whose app lets users geotag potholes to alert city hall when repairs are needed. With this inspiring guide, curious young dreamers can become real inventors with real-world impact.