The book ‘Kotlin In-Depth, Second Edition’ updates all the essential parts of Kotlin and incorporates modern principles, methodologies, and approaches for achieving efficient solutions. The book will guide you to successfully utilize Kotlin in developing JVM apps for desktop, mobile, web platforms and transferring existing Java codebases to Kotlin.The book begins with an introduction to the language and its environment, which will help you to grasp the fundamental concepts underlying Kotlin's design. The readers will learn the Kotlin tooling and the language's core syntax and structures. The book teaches Kotlin's multi-paradigm nature, which enables the creation of powerful abstractions by mixing parts of functional and object-oriented programming. This book discusses how to use standard Kotlin APIs like the standard library, reflection, and coroutine-based concurrency, as well as how to create your flexible APIs using domain-specific languages. The book demonstrates how to use Kotlin for more specific tasks such as testing, developing Android applications, developing Web applications, and developing microservices.