Just over 95% of our Universe comes in the shrouded form of dark energy and dark matter that we can neither explain nor directly detect. Together, these two dark entities play out a cosmic battle of epic proportions, with the gravity of dark matter slowly pulling structures in the Universe together, and dark energy fuelling the Universe's accelerated expansion, making it ever harder for those structures to grow. In this book we will explore this dark enigma and introduce the cosmologist's toolkit of observations and techniques that allow us to confront different theories on the dark Universe. I'll explain why I believe that, to truly understand the dark Universe, we will need some new physics that will forever change our cosmic view.