Throughout the history of science, different thinkers, philosophers and scientists postulated the existence of entities that, in spite of their not being visible or detectable in their time, or perhaps ever, were nevertheless useful to explain the real world. We started this book by looking at a handful of these entities. These included phlogiston to account for fire; the luminiferous ether for propagation of radiation; the homunculus to provide for heredity; and crystalline spheres to carry the wandering planets around the earth. Many of these erroneous beliefs had held up progress, just as dragons drawn on the edges of a map discouraged exploration. This pattern of science evolution continued through the centuries up to the present day. The book evolved into a more extensive history of how science evolved through controversy, suppression, and the desire to maintain the status quo. Our story passes from the Babylonians and Greeks through the middle ages, the renaissance and the scientific revolution to almost current events. We discuss the evolution of our world, the controversy about the extinction of dinosaurs, and open questions in contemporary science such as dark matter, black holes and the origin of the Universe, including how we understand the subatomic world of elementary particles. Most of the chapters deal with astronomy, cosmology and physics, but there are brief ventures into geosciences (continental drift), biosciences (the homunculus), atmospheric physics (Heaviside layer), paleontology (the extinction of dinosaurs), and computer science (artificial intelligence). The authors present a sequence of how mistakes and fallacies have been purged from our quest to understand nature. The way these changes have come about are skillfully set in their relevant historical contexts.