The novel physical properties of topological crystalline insulators (TCIs) make them a versatile platform for exploring topological phenomena and potentialapplications. However, progress in this field has been hindered by the challenge to probe the optical and transport properties of the surface states. In this talk I’ll report our infrared study of a TCI, (001) oriented Pb_0.7Sn_0.3Se in zero and high magnetic fields. We demonstrate that the far-infrared conductivity is dominated by the surface states as a result of their unique band structure and the consequent high surface carrier density. Moreover, our experiments yield a surface mobility of 40,000 cm² V^-1 s^-1. The transport parameters obtained from our experiments suggest the viability of surface-dominated conduction in thin TCI crystals. These findings open up new opportunities for exploring the exotic physics predicted for TCIs.