The book is devoted to the development of programs for mobile devices running the Android operating system. Discusses creating applications using Android system components and services. Provides basic information about the structure of applications, the main classes and their methods, accompanied by code examples. Part 1 contains six chapters describing the basic principles of creating applications, the user interface, application permissions, as well as the base classes: Activity, Intent, Fragment. The book is intended for programmers who are proficient in the Java programming language and want to learn how to write applications running under the Android OS. The book is a translation of publicly available free English-language Internet resources. The second part of the book will cover Notifications, Broadcast Receivers, Threads & AsyncTasks, Alarms, networking, graphics and animation, touch and gesture control, multimedia control, working with sensors, location and mapping, data management, and the ContentProvider and Service classes.