A large Time Projection Chamber (TPC) is the main device for tracking and charged particle identification in the ALICE experiment at the CERN LHC. After the second long shutdown in 2019/20, the LHC will deliver Pb beams colliding at an interaction rate of about 50 kHz, which is about a factor of 50 above the present read-out rate of the TPC. This will result in a significant improvement on the sensitivity of rare probes that are considered key observables to characterize the QCD matter created in such collisions. In order to make full use of this luminosity, a major upgrade of the TPC is required. Since the TPC drift time of 100 μs is 5 times longer than the average time between interactions, the presently employed gating of the TPC wire chambers must be abandoned and continuously operated readout detectors using GEMs will be implemented. To fulfill the challenging requirements of the upcoming upgrade, a novel configuration of GEM detectors has been developed. It allows to maintain excellent particle identification and efficient ion trapping by stacking four GEM foils operated under specific field configuration. Results of an extensive R&D program concerning ion backflow suppression, dE/dx resolution and stability against discharges will be presented. The status of the upgrade of the online calibration and data reduction system, as well as the development of a new readout electronics will be reported. We will also discuss the ongoing detector production.