"The Protestant Ethic and the Spirit of Capitalism" (in the original German, "Die protestantische Ethik und der Geist des Kapitalismus") is a book by German economist and sociologist Max Weber. Written between 1904 and 1905 as a series of essays, it was later expanded by Weber and published in book form in 1920, the year of his death. In it, Weber investigates why capitalism initially developed in countries like England and Germany, concluding that this was due to the worldview and lifestyle instigated by Protestantism at the time. The book was first translated into English by Talcott Parsons in 1930.

It is often argued that this work should not be viewed as a detailed study of Protestantism but rather as an introduction to Weber's later works, especially regarding his studies on the interaction between religious ideas and economic behavior.

In this book, Weber proposes the thesis that Puritan ethics and ideas influenced the development of capitalism. Traditionally, in the Roman Catholic Church, religious devotion was often accompanied by a rejection of worldly matters, including economic pursuits. These conflicts were rooted in asceticism – a devaluation of the body and material detachment. Why was this not the case with Protestantism? Weber addresses this paradox in his work.

He defines the spirit of capitalism as the ideas and habits that ethically favor the rational pursuit of economic gain. Weber claims that this spirit is not exclusive to Western culture, but individuals in other cultures could not, on their own, establish the new economic order of capitalism. As he writes in his essay: "In order for a way of life well-suited to the peculiarities of capitalism to prevail over others (forms of organization), it had to have originated somewhere, not through the actions of isolated individuals, but as a way of life shared by groups of men."