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

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 practised 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.

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 Alan Watts, W. E. B. Du Bois, Edmund Husserl, Bertrand Russell, Ludwig Wittgenstein, Hilary Putnam, and Richard Rorty.

William James was born at the Astor House in New York City on January 11, 1842. He was the son of Henry James Sr., an independently wealthy Swedenborgian theologian well-acquainted with the literary and intellectual elites of his day. The intellectual brilliance of the James family milieu and the remarkable epistolary talents of several of its members have made them a subject of continuing interest to historians, biographers, and critics.

William James received an eclectic transatlantic education, developing fluency in both German and French. Education in the James household encouraged cosmopolitanism. The family made two trips to Europe while James was still a child, setting a pattern that resulted in thirteen more European journeys during his life. James wished to pursue painting; his early artistic bent led to an apprenticeship in the studio of William Morris Hunt in Newport, Rhode Island, but his father urged him to become a physician instead. Since this did not align with James's interests, he stated that he wanted to specialize in physiology. Once he figured this was also not what he wanted to do, he announced he was going to specialize in the nervous system and psychology. James then switched in 1861 to scientific studies at the Lawrence Scientific School of Harvard College.

In his early adulthood, James suffered from a variety of physical ailments, including those of the eyes, back, stomach, and skin. He was also tone deaf. He was subject to a variety of psychological symptoms which were diagnosed at the time as neurasthenia, and which included periods of depression during which he contemplated suicide for months on end.

Two younger brothers, Garth Wilkinson (Wilkie) and Robertson (Bob), fought in the American Civil War. James himself was an advocate of peace. He suggested that instead of youth serving in the military, they serve the public in a term of service "to get the childishness knocked out of them." He took up medical studies at Harvard Medical School in 1864. He took a break in the spring of 1865 to join naturalist Louis Agassiz on a scientific expedition up the Amazon River, but aborted his trip after eight months, as he suffered bouts of severe seasickness and mild smallpox. His studies were interrupted once again due to illness in April 1867. He traveled to Germany in search of a cure and remained there until November 1868; at that time he was 26 years old. During this period, he began to publish; reviews of his works appeared in literary periodicals such as the North American Review.^{[citation needed]}

James finally earned his MD degree in June 1869 but he never practiced medicine. What he called his "soul-sickness" would only be resolved in 1872, after an extended period of philosophical searching. He married Alice Gibbens in 1878. In 1882 he joined the Theosophical Society.