Abstract:       Turbulent transport in the tokamak edge region is studied by using the Global Drift Ballooning code. GDB self-consistently solves drift-reduced Braginskii equations [1] in a 3D annular region from inside the pedestal into the scape-off layer (SOL) in realistic parameter regimes. The model includes an explicit plasma source at the core and a limiter in the SOL. In the L-mode regime, simulations indicates the predominant driver of edge turbulence is the resistive ballooning instability. Studies show that, in agreement with experimental observations, as the density maximum and profile are ramped up, the simulation encounters a density limit regime where the turbulent transport is catastrophically enhanced. On the other hand, as the the temperature profile is increased, the simulation approaches the H-mode regime where turbulent transport is suppressed. These findings seem largely consistent with previous local flux-tube simulation results[2]. Simulations also show that in L-mode plasmas the Boussinesq approximation has little impact on the turbulence structure, fluctuation level and the global profile evolution.