The Varieties of Religious Experience: A Study in Human Nature is a book by Harvard University psychologist and philosopher William James. It comprises his edited Gifford Lectures on natural theology, which were delivered at the University of Edinburgh in Scotland in 1901 and 1902.

The lectures concerned the nature of religion and the neglect of science in the academic study of religion, in James' view. Soon after its publication, the book entered the canon of psychology and philosophy and has remained in print for over a century.

The lectures discussed the distinction between symbolism and reality. Symbols, such as the word "steak" on a menu, do not embody the actuality of the objects they represent. The word "steak" on a menu merely points to some slab of meat in the back of the restaurant. In a similar way, James posits that all of science is fundamentally detached from reality since the tools of science are merely pointers to some actual objective realm. He criticized his audience for the scientific tendency to ignore the unseen aspects of life and the universe. As an example, he discussed the way the notion of a lemon causes salivation in the mouth of an individual; while there is no lemon, there is clearly a process occurring worthy of academic inquiry.

William James Mayo (June 29, 1861 – July 28, 1939) was a physician and surgeon in the United States and one of the seven founders of the Mayo Clinic. He and his brother, Charles Horace Mayo, both joined their father's private medical practice in Rochester, Minnesota, USA, after graduating from medical school in the 1880s. In 1919, that practice became the not-for-profit Mayo Clinic.