This book describes in a concise form the complete process of creating applications for smartphones and tablets. The features of mobile operating systems and devices, the selection of development tools, the preparation of working documentation in the spirit of Agile, the design of the structure and architecture of the solution, the creation of an automated Continues Integration/Continues Delivery pipeline, as well as monitoring the performance of the final product on the devices of real users are considered. All examples are given in C#. The publication can be recommended to both experienced and novice programmers interested in developing mobile applications. It can also be used as a manual in universities, continuing education centers, etc.