Atomic Kotlin
Atomic Kotlin is the book and associated learning resources by Bruce Eckel and Svetlana Isakova.
Version 1.1 (November 2021) includes updates for Kotlin 1.5 (works with 1.6) and all corrections/clarifications since the original release.
JetBrains Connect, Episode 4 – “Why Kotlin?” with Bruce Eckel and Svetlana Isakova