This Stanford Continuing Studies course is a six-quarter sequence of classes exploring the essential theoretical foundations of modern physics. The topics covered in this course focus on classical mechanics, quantum mechanics, the general and special theories of relativity, electromagnatism, cosmology, black holes and statistical mechanics. While these courses build upon one another, each section of the course also stands on its own, and both individually and collectively they will allow the students to attain the "theoretical minnimum" for thinking intelligently about physics. Quantum theory governs the universe at its most basic level. In the first half of the 20th century physics was turned on its head by the radical discoveriies of Max Planck, Albert Einstein, Niels Bohr, Werner Heisenberg, and Erwin Schroedinger. An entire new logical and mathematical foundation - quantum mechanics - eventually replaced classical physics. This course explores the quantum world, including the particle theory of light, the Heisenberg Uncertainty Principle, and the Schroedinger Equation. The course is taught by Leonard Susskind, the Felix Bloch Professor of Physics at Stanford University.