This paper examines the role of loading frequency and temperature on intergranular crack growth in an advanced P/M superalloy. This is achieved by conducting a series of dwell-fatigue crack growth experiments at temperatures of 650°C, 704°C and 760°C in air. The loading cycles consist of fatigue cycles with a frequency of 0.33 Hz having a dwell time superimposed at the maximum load level. The dwell time ranged from 0 seconds to 7200 seconds. The role of the loading frequency has been examined by correlating the slip line density and its influence on the transition between transgranular and intergranular fracture modes.  Results of the dwell-fatigue crack growth tests show that, for frequencies below the transitional frequency, the length of the dwell time does not influence the crack growth rate.  With a focus on the intergranular fracture, its mechanism has been described in terms of grain boundary deformation involving boundary sliding-cavitation processes. This mechanism has been modeled using a two dimensional cohesive zone model in which the continuum behaviour is described by a macroscopic internal state variable model for the crack tip far field region and by a coarse scale polycrystal plasticity model in the crack tip near region.  The grain boundary interface has been modeled using traction-displacement laws accounting for deformation in both tangential and normal directions. Results of crack growth tests in vacuum have been used to establish a grain boundary fracture criterion as a function of both temperature and environment.  Results of the numerical modeling of intergranular cracking are compared with those obtained experimentally for different applied load conditions.  This comparison provides a basis for determining the critical grain boundary sliding displacement and its degradation as a function of environment related oxygen concentration.