Kotlin is one of the newest languages in the Java ecosystem, removing many of the limitations of Java and being much more generic. Among its advantages: full compatibility with Java and the ability to integrate at the source code level, wide support for the functional programming paradigm, which helps to write reliable and secure code, laconicism of syntax, and, very importantly, guarantees of support from the IT giant Google. Pierre-Yves Somon. an experienced Java developer, in his book he covers in detail the nuances of programming in Kotlin, moving from a general description of the language to its characteristic features and capabilities, including functional programming techniques. The publication is intended for developers familiar with Java and seeking to improve the security of their programs, as well as simplify their writing, testing and maintenance.