Topological insulators are a predicted new quantum state of matter in which spin-orbit coupling gives rise to topologically protected surface states with unpaired spin-helical Dirac cones. Topological insulators are predicted to have exotic properties including Majorana fermions induced by the proximity effect from a superconducting film, a quantized magnetoelectric effect and hybridized spin-plasmon modes. The topological magneto-electric effect leads to a Faraday rotation quantized in units of the fine structure constant. I will describe experiments designed to measure the Faraday rotation in Bi2Se3, one of the best current examples of a topological insulator.