String theory is at present the leading candidate for the "theory of everything"—one that encompasses all fundamental particles and forces in the universe. Physicist John M. Pierre, now at Datafusion in San Francisco, provides an online tutorial on string theory, introducing the theory's basic concepts and illuminating some of its intricacies. Find out about Planck mass, gravitons, D-branes, supersymmetry, supergravity, and much more.