Written by a well-known author in the field, this book presents a modern understanding of the universe based on relativity, quantum physics and their elusive combination. It introduces the crucial theoretical ingredients in an accessible way, starting from the physics of Newton and developing subsequent theories all the way to the modern enigma of quantum gravity. The intermediate level presentation assumes only a general knowledge of math and physics, adopting a "two-level" approach: equations are retained throughout the chapters but set apart from the main text in boxes to allow for lay readers to understand the book. For scientists, researchers, students and lecturers in cosmology, astronomy, gravitation, quantum and theoretical physics; as well as mathematicians, students, lecturers, academics and non-experts in related fields with an interest in the subject.