The Feynman Lectures on Physics is a physics textbook based on some lectures by Richard P. Feynman, a Nobel laureate who has sometimes been called "The Great Explainer". The lectures were given to undergraduate students at the California Institute of Technology (Caltech), during 1961–1963. The book's authors are Feynman, Robert B. Leighton, and Matthew Sands. In 2013, Caltech made the book freely available, on the web site feynmanlectures.caltech.edu.