This is, as its title says, a book about nonsense-in particular the kinds which most appeal to us today. UFOs; ESP or psi phenomena generally; and the perennially popular ideas of Dr. Velikovsky. Do UFOs exist? Are the Russians about to revolutionize modern warfare with their psi machines? Can we project our thoughts alone a fifth dimension and foresee the market crash coming next week? Was there really an explosion of psychic energy in a nearby bookcase one day when Drs. Freud and Jung were having a heated discussion? Is it safe to assume, with Velikovsky, that a good deal of our petroleum fell down recently from the sky? Some of these ideas have established quite a following-and there is always a possibility, of course, that not all of them are rubbish. Our government seems to be discreetly funding research in ESP on the chance that it may have some military potential. The sightings of UFOs go on and on. And now a few scientists are beginning to have second thoughts about Velikovsky. So I felt I should try to show why these items of the New Nonsense may actually be that. In fact, if some of what I have called nonsense proves to be, neither my main argument nor the attitude of the believing public will be much affected. It is important to understand why millions of supposedly educated people have not done so. The real question is what the resurgence of nonsense in our era means. What connection, if any, does it have with the revolutionary spirit of the age? And what, therefore, may it prophesy?