The concept of cultural insanity provides a better way of understanding much of what is wrong in our society and in the world today--and how it got that way. Where our own culture is involved, we are partly blind to it. Accordingly, correctly grasping the idea of cultural insanity will also reveal pathways to develop more realistic worldviews, improve our self-understanding, and help liberate our minds from the unseen mesh of cultural implants and biases. Surprisingly, cultural insanity can be characterized by features of a society/culture that unnecessarily thwart the development of human potential. Development potentials are outlined. Because "unnecessarily thwart" means that there must be viable alternatives, allowances are made for a culture's level of technology, its people's levels of consciousness, and more. Part One includes the theory and methods for cultural insanity analyses, along with many examples of current and recent cultural insanities from U.S. politics, history and the environmental realm. Parts Two through Four are historical case studies that consider witch-hunts, religion vs. science in the Middle Ages, and the discoveries of geologic time and evolution. With the distance in time to keep bias at bay, the reader can better see a cultural retrogression toward greater cultural insanity; a culture that resisted possibilities to advance human potential; and a once-buried cultural insanity that became fully exposed--but is still present today. The causes of cultural insanity are to some extent rooted in the evolutionary history of our species, including the way our brains operate—and thus affect all cultures. Awareness of the nature of these processes, along with more fully conscious thinking, and the use of evidence, reason and scientific methods, can help us to reduce the negative effects these influences have on our societies and culture(s), to envision better alternatives to improve the development of human potential, and to reduce humanity’s planetary devastation.