William James (January 11, 1842 – August 26, 1910) was an American philosopher, historian, and psychologist, and the first educator to offer a psychology course in the United States. James is considered to be a leading thinker of the late 19th century, one of the most influential philosophers of the United States, and the "Father of American psychology".

Along with Charles Sanders Peirce, James established the philosophical school known as pragmatism, and is also cited as one of the founders of functional psychology. A Review of General Psychology analysis, published in 2002, ranked James as the 14th most eminent psychologist of the 20th century. A survey published in American Psychologist in 1991 ranked James's reputation in second place, after Wilhelm Wundt, who is widely regarded as the founder of experimental psychology. James also developed the philosophical perspective known as radical empiricism. James's work has influenced philosophers and academics such as Émile Durkheim, W. E. B. Du Bois, Edmund Husserl, Bertrand Russell, Ludwig Wittgenstein, Hilary Putnam, Richard Rorty, and Marilynne Robinson.

Born into a wealthy family, James was the son of the Swedenborgian theologian Henry James Sr. and the brother of both the prominent novelist Henry James and the diarist Alice James. James trained as a physician and taught anatomy at Harvard, but never practiced medicine. Instead, he pursued his interests in psychology and then philosophy. He wrote widely on many topics, including epistemology, education, metaphysics, psychology, religion, and mysticism. Among his most influential books are The Principles of Psychology, a groundbreaking text in the field of psychology; Essays in Radical Empiricism, an important text in philosophy; and The Varieties of Religious Experience, an investigation of different forms of religious experience, including theories on mind-cure.