This book is an introduction to gravitational waves and related astrophysics. It provides a bridge across the range of astronomy, physics, and cosmology that comes into play when trying to understand the gravitational-wave sky. Starting with Einstein's theory of gravity, chapters develop the key ideas step by step, leading up to the technology that finally caught these faint whispers from the distant Universe. The second part of the book makes a direct connection with current research, introducing the relevant language and making the involved concepts less 'mysterious'. The book is intended to work as a platform, low enough that anyone with an interest in gravitational waves can scramble onto it, but at the same time high enough to connect readers with active research-and the many exciting discoveries that are happening right now.