With Google's announcement at the I/O Conference in 2017 to make Kotlin an official language for Android, Kotlin has been gaining popularity among developers around the world.

However, Kotlin's use and popularity aren't limited to the Android community. Many other communities, such as the desktop, web, and backend community are embracing Kotlin too. Many new libraries and frameworks are being created and existing ones are providing support for Kotlin.

With more developers coming to the Kotlin community and with its natural flexibility, more programming styles are being tried. The purpose of this book is to introduce the functional programming style to the wide Kotlin community, leading and guiding on the first steps, and giving the basic tools to progress further to more advanced concepts.