Three dimensional topological insulators are a novel quantum state of matter which exhibits an insulating bulk state and gapless metallic surface. Owing to the large spin-orbit interaction and the ensuing band structure topology, these surface states behave as massless, spin-helical Dirac fermions that are protected against backscattering. In this talk I present recent results of magnetotransport measurements performed on the 3D topological insulator Bi2Se3. The samples studied are nano-connected ultra-thin flakes of high quality Bi2Se3 deposited on a SiO2/Si substrate that acts as a gate electrode. Such back-gated device allows to vary continuously the carrier density by electrostatic doping over the entire Dirac cone of the surface state. Under magnetic field B, sweeping the gate voltage enables us to control the filling of the Landau levels, resulting in Shubnikov-de Haas oscillations of the conductance. The continuous evolution of the SdH oscillations from electron to hole character gives a clear evidence for the Dirac nature of the surface state. After this demonstration of the control of electronic transport through the surface states I’ll show that, when the electrodes are superconducting at B=0, Cooper pairs can also be transferred into the surface state leading to a gate-tuned ambipolar supercurrent.