The topological surface states in 3D materials predicted by Kane, Mele and Fu were rapidly detected by surface sensitive spectroscopy (ARPES and STM). Transport experiments to investigate their properties have been more challenging. Following a brief introduction, I will survey experiments in which the surface states were first detected by magnetoresistance oscillations in Bi2Se3 and Bi2Te3. More recently, the hybrid Bi2Te2Se has emerged as the most attractive candidate for transport experiments. I will describe a recent experiment showing that the occupation of the surface Dirac cone can be tuned by liquid gating.