Kotlin is a powerful and pragmatic language, but it's not enough to know about its features. We also need to know when they should be used and in what way. This book is a guide for Kotlin developers on how to become excellent Kotlin developers. It presents and explains in-depth the best practices for Kotlin development. Each item is presented as a clear rule of thumb, supported by detailed explanations and practical examples. Effective Kotlin provides insights into the idiomatic way of Kotlin development, as well as many general programming best practices and details about advanced Kotlin features like DSL creation, generics, platform types or inline functions and classes. All that for experienced Kotlin developers to get more effective when they use this programming language: to make safe, well designed and efficient code. The purpose of this book To really unleash the advantages of Kotlin, we need to use it properly. To do so, not only do we need to know about different Standard Library (stdlib) functions but even more, we need a good understanding of Kotlin features, purpose, and design. The main goal of this book is to explain how to use different Kotlin features to achieve safe, readable, scalable, and efficient code. Since this book is written to help developers get better at writing code, it also touches many general rules for programmers. This book tries to compose as much knowledge about best practices in Kotlin as possible. You can call it a collection of best practices. For whom the book is written This book is not teaching basics. It assumes that you have enough knowledge and skills to do Kotlin development. If you dont, I recommend starting first from resource designed for beginners. Effective Kotlin is directed to experienced Kotlin developers. Though I will assume that even experienced developers might not know some features. This is why I explain some concepts like: Property Platform type Named arguments Property delegation DSL creation Inline classes and functions Tail recursion I want this book to be a complete guide for Kotlin developers on how to become an amazing Kotlin developer.