"Memoirs of Extraordinary Popular Delusions and the Madness of Crowds" by Charles Mackay is an early study of crowd psychology first published in 1841. This journalistic work examines humanity's susceptibility to collective manias through three volumes exploring financial bubbles, religious crusades, witch trials, alchemy, and countless other follies. Mackay debunks popular delusions with colorful anecdotes and sensational storytelling, from Dutch tulip mania to the influence of politics on beard styles. His analysis of economic bubbles remains influential, credited with helping financiers predict market crashes and understand modern speculation.