The Know-It-All: One Man's Humble Quest to Become the Smartest Person in the World is a book by Esquire editor A. J. Jacobs, published in 2004.

It recounts his experience of reading the entire Encyclopædia Britannica; all 32 volumes of the 2002 edition, extending to over 33,000 pages with some 44 million words. He set out on this endeavour to become the "smartest person in the world". The book is organized alphabetically in encyclopedia format and recounts both interesting facts from the encyclopedia and the author's experiences.