Described by the philosopher A.J. Ayer as a work of `great originality and power`, this book revolutionized contemporary thinking on science and knowledge. Ideas such as the now legendary doctrine of `falsificationism` electrified the scientific community, influencing even working scientists, as well as post-war philosophy. This astonishing work ranks alongside The Open Society and Its Enemies as one of Popper`s most enduring books and contains insights and arguments that demand to be read to this day.